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Improving the superconductivity of thin films, especially the critical current density (JC) and the critical field (HC), is crucial for the application of superconducting devices. Here, we apply a ...

Two-dimensional transition metal dichalcogenides (TMDs) are important materials for promising electronic devices because they usually exhibit excellent and highly tunable electronic properties. Here, we report on the pressure-driven electronic phase transition in a TMD 1

Understanding the interplay among different magnetic exchange interactions and its physical consequences, especially in the presence of itinerant electrons and disorder, remains one of the central themes in condensed matter physics. In this vein, the coupling between antiferromagnetic and spin-glass orders may lead to large exchange bias, a property with potential broad technological applications. In this paper, we report the coexistence of antiferromagnetic order and spin-glass behaviors in the quasi-one-dimensional iron telluride ${\mathrm{TaFe}}_{1+x}{\mathrm{Te}}_{3}$ ($x=0.25$). Its antiferromagnetism is believed to arise from the antiferromagnetic interchain coupling between the ferromagnetically aligned FeTe chains along the $b$ axis, while the spin-glassy state stems from the disordered Fe interstitials. This dichotomic role of chain and interstitial sublattices is responsible for the large exchange bias observed at low temperatures, with the interstitial Fe acting as the uncompensated moment and its neighboring Fe chain providing the source for its pinning. This iron-based telluride may thereby represent a paradigm to study the large family of transition metal chalcogenides whose magnetic order or even dimensionality can be tuned to a large extent, forming a fertile playground to manipulate or switch the spin degrees of freedom thereof.

Single crystalline Selenium (Se) nanoribbons with large length-diameter ratio was catalytically synthesized by laser ablation in liquids. In this study, the unique growth, pressure-dependent phase evolution and superconducting transition of Se nanoribbons are systematically investigated. Importantly, we first found that the semiconductor-metal transition pressure of such Se nanoribbons located at 11.1 GPa at room temperature, which was extremely close to the theoretically predicated value of 11.16 GPa of hexagonal Se. The structure evolution of Se nanoribbons revealed via in situ Raman spectrum indicated three subsequent phase transition stages. The temperature dependence of resistance measurements revealed the occurrence of superconducting state of monoclinic Se at 11.8 GPa, which is markedly lower than reported pressures to date. The phase transition barrier attenuation originating from the volumetric contraction of Se lattice is assumed to offset the influences of temperature and surface energy in low-dimensional Se nanoribbons with large length-diameter ratios, resulting in a transition pressure approaching the predicted value.

The quasi-two-dimensional kagome superconductors $A$V${}_{3}$Sb${}_{5}$ ($A$ $=$ K, Rb, and Cs) have attracted great interest due to various exotic quantum phenomena, such as topological charge density waves and the giant anomalous Hall effect. Here, the authors find two-dome unconventional superconductivity in CsV${}_{3}$Sb${}_{5}$ under high pressure. They also confirm the absence of a structural phase transition up to 43.1 GPa through high-pressure synchrotron x-ray diffraction measurements, suggesting that the novel reemergent superconductivity dome can be attributed to the Fermi surface reconstruction caused by the Lifshitz transition.

Copper monotelluride CuTe has a layered orthorhombic structure (space group Pmmn, No. 59) but exhibits a quasi-one-dimensional charge density wave (CDW) order. Here, we present a high-pressure study of CuTe in a diamond anvil cell at pressures up to 41.8--49.8 GPa, through a combination of electrical transport, synchrotron x-ray diffraction (XRD), and Raman spectroscopy measurements as well as theoretical calculations. Our transport experiments show that the CDW transition is manifested as a hump in resistivity; with the application of external pressure, its transition temperature ${T}_{\mathrm{CDW}}$ decreases gradually and the amplitude of the resistivity hump decays rapidly. The CDW gets suppressed completely above \ensuremath{\sim}10 GPa as estimated by a linear extrapolation of the ${T}_{\mathrm{CDW}}$ versus $P$ trend. Upon further compression, a sudden drop in resistivity is initially observed at \ensuremath{\sim}2.4 K and \ensuremath{\sim}20 GPa, and zero resistance is established above \ensuremath{\sim}37 GPa, suggesting the occurrence of superconductivity (SC). Combined XRD and Raman data as well as theoretical calculations together evidence that the emergence of SC at \ensuremath{\sim}20 GPa is accompanied by an orthorhombic to monoclinic (space group $\mathit{Cm}$, No. 8) structural transition.

Chalcopyrite II-IV-V2 semiconductors are promising materials in nonlinear optical, optoelectronic, and photovoltaic applications. In this work, pressure-tailored optical properties as well as pressure-driven emergent superconductivity in chalcopyrite ZnSiP2 are reported via photoluminescence (PL) spectroscopy and electrical transport experiments. During compression, the PL peak energy exhibits a plateau between 1.4 and 8.7 GPa, which is accompanied by a piezochromic transition and correlated with the progressive development of cation disorder. Upon further compression across a phase transition from tetragonal to cubic rock-salt structure, superconductivity with a critical temperature Tc ~ 8.2 K emerges immediately. Tc decreases in the range of 24.6–37.1 GPa but inversely increases at higher pressures, thereby exhibiting an unusual V-shaped superconducting phase diagram. These findings present vivid structure–property relationships, which not only offer important clues to optimize the optical and electronic properties, but also provide a new way to use compression to switch between different functionalities. A semiconductor that is compatible with silicon but has better optical properties has been fully characterized by researchers in China. Silicon is perhaps the best-known example of a semiconductor but is not good at emitting light. Scientists continue to identify and characterize alternatives that might be better suited for specific applications. Yifang Yuan from the High Magnetic Field Laboratory in Hefei and co-workers have investigated in detail the properties of semiconducting zinc-silicon-phosphorus. ZnSiP2 is a member of a class of materials known as chalcopyrites and is compatible with and can be grown on silicon but is better at generating light. The team studied how external pressure affects the semiconductor’s structural, optical and electronic properties. They showed that at a sufficiently high pressure, the semiconductor exhibits superconducting behavior. Pressure engineered optical properties as well as presssure induced emergent superconductivity are revealed in II-IV-V2 semiconductor ZnSiP2, which demonstrate vivid structure–property relationships. Especially, along with a structural phase transition from tetragonal to cubic phase under compression, ZnSiP2 evolves from a photovoltaic semiconductor into a superconductor.

Materials with nonsaturating, extremely large magnetoresistance (XMR) attract continuous research interest due to their great potential in the fields of spintronics and magnetic sensors/switches. Here, we report the discovery of pressure-driven superconductivity (SC) in trigonal ${\mathrm{PtBi}}_{2}$, a semimetal material with nontrivial triply degenerate point fermions exhibiting a nonsaturating XMR effect, above a critical pressure of $\ensuremath{\sim}5--6$ GPa. The superconducting transition onset temperature is $\ensuremath{\sim}2$ K and displays a very weak pressure dependence across a broad pressure range of $\ensuremath{\sim}5--48$ GPa. The lattice structure of trigonal ${\mathrm{PtBi}}_{2}$ is stable against pressure at least to 12.9 GPa. Around the same critical pressure where the SC emerges, the Hall coefficient varies violently and shows a sign crossover from low pressure positive (hole dominated) to high pressure negative (electron dominated), probably indicating a close relationship between them.

We report on pressure tuning of superconductivity in a strongly coupled superconductor ${\mathrm{Mo}}_{8}{\mathrm{Ga}}_{41}$ with a critical temperature ${T}_{c}\ensuremath{\sim}9.8\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Resistance measurements show that ${T}_{c}$ is suppressed to 3.6 K at 19 GPa followed by a nonmonotonic variation at higher pressures. Synchrotron x-ray diffraction experiments reveal an amorphization taking place at the critical pressure ${P}_{c}\ensuremath{\sim}19\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. As comparing with $\mathrm{Mg}{\mathrm{B}}_{2}$, the ${\mathrm{Mo}}_{8}{\mathrm{Ga}}_{41}$ shows a relative low decreasing rate of ${T}_{c}$, which might be attributed to its unique vertex-sharing type of cluster architecture. Survival of superconductivity across the crystalline to amorphous transition indicates that, although long-range structural order of endohedral Ga clusters is destroyed, short-range-ordered intracluster structure still exists and allows for local Cooper pairing. Due to presence of disorders in the amorphous phase, establishment of Cooper pair coherence is shifted to lower temperatures, which causes unusual transport behaviors near ${T}_{c}$, e.g., the anomalous resistance peak and dip. The amorphous superconducting phase is able to be retained to ambient pressure and therefore provides an ideal platform to study disorder effects on superconductivity.

It is commonly anticipated that an insulating state will collapse in favor of an emergent metallic state at high pressures: The average electron density must increase with pressure, while the electronic bandwidth is expected to broaden and fill the insulating energy band gap. Here we report an unusually stable insulating state that persists up to at least 185 GPa in $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$, the archetypical spin-orbit-driven ${J}_{\mathrm{eff}\phantom{\rule{0.28em}{0ex}}}=1/2$ insulator. This study shows that the electrical resistance R of single-crystal $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ initially decreases with applied pressure P, reaches a minimum in the range 32--38 GPa, then abruptly rises to recover the insulating state with increasing P up to 185 GPa. However, evidence of a saturation of R below 80 K for $P\ensuremath{\ge}124\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ GPa raises the possibility of a low-temperature exotic state. Our synchrotron x-ray diffraction and Raman scattering data show the emergence of the rapid increase in R is accompanied by a structural phase transition from the native tetragonal $I{4}_{1}/acd$ phase to an orthorhombic $Pbca$ phase (with much reduced symmetry) at 40.6 GPa. The clear correspondence of the onset pressures of these two anomalies is key to understanding the stability of the insulating state at megabar pressures: Pressure-induced, structural distortions prevent the expected onset of metallization, despite the sizable volume compression attained at the highest pressure accessed in this study.

Crystalline and amorphous structures are two of the most common solid-state phases. Crystals having orientational and periodic translation symmetries are usually both short-range and long-range ordered, while amorphous materials have no long-range order. Short-range ordered but long-range disordered materials are generally categorized into amorphous phases. In contrast to the extensively studied crystalline and amorphous phases, the combination of short-range disordered and long-range ordered structures at the atomic level is extremely rare and so far has only been reported for solvated fullerenes under compression. Here, a report on the creation and investigation of a superconducting quasi-1D material with long-range ordered amorphous building blocks is presented. Using a diamond anvil cell, monocrystalline (TaSe 4 ) 2 I is compressed and a system is created where the TaSe 4 atomic chains are in amorphous state without breaking the orientational and periodic translation symmetries of the chain lattice. Strikingly, along with the amorphization of the atomic chains, the insulating (TaSe 4 ) 2 I becomes a superconductor. The data provide critical insight into a new phase of solid-state materials. The findings demonstrate a first ever case where superconductivity is hosted by a lattice with periodic but amorphous constituent atomic chains.

Band engineering in layered transition metal dichalcogenides (TMDs) leads to a variety of emergent phenomena and has obtained considerable attention recently. Transition metal ditelluride ${\mathrm{NiTe}}_{2}$ has been discovered experimentally to be a type-II Dirac semimetal at ambient pressure, and was predicted to display superconductivity in the monolayer limit. Here we systematically investigate the structural and electronic properties of type-II Dirac semimetal ${\mathrm{NiTe}}_{2}$ under high pressure. Room-temperature synchrotron x-ray diffraction and Raman scattering measurements reveal the stability of the pristine hexagonal phase up to 52.2 GPa, whereas both the pressure coefficient and linewidth of Raman mode ${E}_{g}$ exhibit anomalies at a critical pressure ${P}_{\mathrm{c}}\ensuremath{\sim}16\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$. Meantime, Hall resistivity measurement indicates that the hole-dominated behavior maintains up to 15.6 GPa and transforms into electron-dominated behavior at higher pressures. Our findings consistently demonstrate a pressure-induced Lifshitz transition in type-II Dirac semimetal ${\mathrm{NiTe}}_{2}$.

We have performed in-plane electrical transport and polarized Raman spectroscopy measurements on layered material CuTe to characterize the quasi-one-dimensional charge density wave (CDW). Along with the CDW formation below TCDW ∼346 K, the a-axis resistivity shows a huge hump, but the b-axis resistivity exhibits no evident anomaly, manifesting the quasi-one-dimensional character of the CDW. Concomitantly, a rapid rise in positive Hall coefficient is observed due to partial gaping out of the Fermi surface. Based on our Raman scattering measurement, we observe two Raman-active phonon modes in the non-CDW state and, additionally, one collective amplitude mode and four zone-folded modes in the CDW state. The phonon-mode shift with temperature clearly deviates from the expected anharmonic model upon approaching TCDW, suggesting strong electron–phonon coupling in driving the CDW transition. The amplitude mode even survives at room temperature and above, whose evolution can be described by a modified mean-field model, indicating a well-defined CDW order. These results, in addition to the simple formula and easy-to-exfoliate layered structure, promise CuTe as a model system to study the Peierls-like CDW physics and hold great potentials for CDW-based applications.

We performed in situ high-pressure synchrotron x-ray diffraction (XRD) and electrical transport measurements on topological semimetal TaSb2 in diamond anvil cells with pressures up to 60.0–63.0 GPa. No evident trace of structural phase transitions is observed from our XRD. A fit of the volume versus pressure data by using the third-order Birch–Murnaghan equation of state yields the bulk modulus B 0 = 131.2 ± 3.4 GPa and its first-order derivative B 0 ′ = 6 ± 0.3. From ambient pressure to 27.8 GPa, the low-temperature conduction behaviors of TaSb2 stay almost unchanged, exhibiting a power law with the exponent around 3; meanwhile, the magnetoresistance (MR) at 5 K follows a same relationship of MR∝Bm with m= 1.45 ± 0.10. These results imply that the topological semimetal state of TaSb2 may be robust subjected to pressure, at least to 27.8 GPa.

Topological semimetal, a novel state of quantum matter hosting exotic emergent quantum phenomena dictated by the nontrivial band topology, has emerged as a new frontier in condensed-matter physics. Very recently, the coexistence of triply degenerate points of band crossing and Weyl points near the Fermi level was theoretically predicted and experimentally identified in MoP. Via high-pressure electrical transport measurements, we report here the emergence of pressure-induced superconductivity in MoP with a critical transition temperature Tc of ca. 2.5 K at ca. 30 GPa. No structural phase transition is observed up to ca. 60 GPa via synchrotron X-ray diffraction study. Accordingly, the topologically nontrivial band protected by the crystal structure symmetries and superconductivity are expected to coexist at pressures above 30 GPa, consistent with density functional theory calculations. Thus, the pressurized MoP represents a promising candidate of topological superconductor. Our finding is expected to stimulate further exploitation of exotic emergent quantum phenomena in novel unconventional fermion system. Molybdenum phosphide becomes superconducting above 30 GPa, with a critical transition temperature of 2.5 K. A team led by Youguo Shi, Xiaoping Yang and Zhaorong Yang from the Chinese Academy of Sciences perform high-pressure electrical transport measurements in molybdenum phosphide, which is a recently proved topological material hosting exotic fermions. They apply pressure over 90 GPa and observe a superconducting transition above 30 GPa with a critical transition temperature of 2.5 K, which increases to 4 K at 95 GPa. Meanwhile, the compound crystalizes into a (tungsten carbide) WC-type structure where the topological properties are predicted from ambient pressure up to 60 GPa. They expect that topological fermions and superconductivity could coexist under a pressure between 30 GPa and 60 GPa, suggesting a possible candidate for topological superconductivity.

Noncentrosymmetric molybdenum nitride $\mathrm{R}{\mathrm{h}}_{2}\mathrm{M}{\mathrm{o}}_{3}\mathrm{N}$ is a conventional $s$-wave superconductor at ambient pressure. Here we report the evolution of structural and electronic properties of $\mathrm{R}{\mathrm{h}}_{2}\mathrm{M}{\mathrm{o}}_{3}\mathrm{N}$ under high pressure. X-ray diffraction measurements reveal the stability of pristine \ensuremath{\beta}-Mn-type cubic structure up to 47.9 GPa, accompanied by the continuously enhanced distortion of $\mathrm{M}{\mathrm{o}}_{6}\mathrm{N}$ octahedra. Electronic transport experiments show the robustness of superconductivity under pressure, i.e., the superconducting transition temperature ${T}_{\mathrm{c}}$ varies only \ensuremath{\sim}0.7 K upon compression up to 38.5 GPa. Meanwhile, detailed analyses of both structural and transport results consistently reveal a critical pressure of \ensuremath{\sim}14.0 GPa. In agreement with the enhancement of octahedral distortion, the temperature dependence of upper critical magnetic field accords with a $p$-wave model at 22.0 GPa and an $s$-wave model at 6.0 GPa. These results suggest the emergence of novel superconductivity in the distorted $\mathrm{R}{\mathrm{h}}_{2}\mathrm{M}{\mathrm{o}}_{3}\mathrm{N}$ cubic phase under pressure, which could be attributed to the enhanced strength of antisymmetric spin-orbit coupling (ASOC) via pressure-modified local octahedral distortion. Our findings may shed light on the searching and understanding of unique triplet-pairing superconductivity in other inversion-broken superconductors with strong ASOC.

We report a systematic high-pressure study of magnetic topological semimetal ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ through measurements of synchrotron x-ray diffraction (XRD), magnetization, electrical, and Hall transports combined with first-principle theoretical calculations. No evident trace of structural phase transition is detected through synchrotron x-ray diffraction over the measured pressure range of 0.2--50.9 GPa. We find that the ferromagnetism and the anomalous Hall resistivity are monotonically suppressed as increasing pressure and almost vanish around 22 GPa. The anomalous Hall conductivity varies nonmonotonically against pressure at low temperatures, involving competition between original and emergent Weyl nodes. Combined with first-principle calculations, we reveal that the intrinsic mechanism due to the Berry curvature dominates the anomalous Hall effect under high pressure.

We present a high-pressure study of type-II Dirac semimetal PtSe

Bulk $1T\text{\ensuremath{-}}\mathrm{TiT}{\mathrm{e}}_{2}$ (hexagonal, space group P-$3m1$) exhibits semimetallic conductivity with weak Anderson localization characteristic at ambient pressure, but superconductivity under high pressure of $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. Here the detailed evolutions of structural and transport properties in $\mathrm{TiT}{\mathrm{e}}_{2}$ during compression are investigated by extending pressure up to 50.2 GPa. The combined high-pressure electrical transport and synchrotron x-ray diffraction experiments unravel two critical pressure points. At ${P}_{c1}\ensuremath{\sim}5.4\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, the superconductivity emerges, which is accompanied by a structural transition from $P\text{\ensuremath{-}}3m1$ to a mixture of $P\text{\ensuremath{-}}3m1$ and monoclinic $C2/m$ phase. The localization effect maintains until the structural transition is over at ${P}_{c2}\ensuremath{\sim}19.1\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, meanwhile the Hall coefficient ${R}_{\mathrm{H}}$ changes from positive to negative. Our results demonstrate that the superconductivity in the pressurized $\mathrm{TiT}{\mathrm{e}}_{2}$ can be assigned to the high-pressure $C2/m$ phase which is electron dominated.

© 2019 American Physical Society. We report on the pressure-driven superconductor-insulator transition in heavily boron-doped nanodiamond films. By systematically increasing the pressure, we suppress the Josephson coupling between the superconducting nanodiamond grains. The diminished intergrain coupling gives rise to an overall insulating state in the films, which is interpreted in the framework of a parallel-series circuit model to be the result of bosonic insulators with preserved localized intragrain superconducting order parameters. Our investigation opens up perspectives for the application of high pressure in research on quantum confinement and coherence. Our data unveil the percolative nature of the electrical transport in nanodiamond films, and highlight the essential role of grain boundaries in determining the electronic properties of this material. ispartof: PHYSICAL REVIEW MATERIALS vol:3 issue:3 status: published

Both $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ and $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ are superconductors with topological nontrivial signs. Here we report that the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ superconductor is converted by pressure into the \ensuremath{\beta}-phase superconducting polymorph, with the superconductivity being further enhanced upon decompression. Through high-pressure resistance and synchrotron x-ray-diffraction experiments, we show that the \ensuremath{\alpha} phase transforms into the \ensuremath{\beta} phase at ${P}_{c}\ensuremath{\sim}8$ GPa, above which the superconductivity is robust up to the maximum pressure investigated in this work. More interestingly, when the applied pressure is gradually released from 42.9 down to 1.7 GPa, the ${T}_{c}$ increases monotonously from 2.5 to 4.0 K. We argue that the observed unusual evolution of superconductivity can be explained by combination of pressure-manipulated crystal quality and the pressure dependence of ${T}_{c}$ of the $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{PdB}{\mathrm{i}}_{2}$ superconductor.

Layered lanthanum silver antimonide LaAgSb2 exhibits both charge density wave (CDW) order and Dirac-cone-like band structure at ambient pressure. Here, we systematically investigate the pressure evolution of structural and electronic properties of LaAgSb2 single crystal. We show that the CDW order is destabilized under compression, as evidenced by the gradual suppression of magnetoresistance. At P C ∼ 22 GPa, synchrotron x-ray diffraction and Raman scattering measurements reveal a structural modification at room-temperature. Meanwhile, the sign change of the Hall coefficient is observed at 5 K. Our results demonstrate the tunability of CDW order in the pressurized LaAgSb2 single crystal, which can be helpful for its potential applications in the next-generation devices.

The p-type CdCr2Se4 exhibits semiconducting conductivity while n-type CdCr2Se4 displays a semiconductor–metal transition and a concomitant colossal magnetoresistance near the Curie temperature. Here, we investigate the pressure effect on the conductivity for both types of compounds. We show that the resistance of p-type sample decreases continuously upon compression, while the semiconducting behavior dominates up to 27.9 GPa. For the n-type sample, the semiconductor-metal transition is suppressed gradually with the increase in pressure; meanwhile, the magnetoresistance becomes less and less pronounced and is negligible at 9.2 GPa. Combined with in situ high-pressure magnetization, x-ray diffraction, and Raman spectra investigations, a ferromagnetic ground state is deduced in the pressurized n-type CdCr2Se4 before the structural transition, which is in stark contrast to the pressure effect on n-type HgCr2Se4.

The geometrically frustrated iridate La3Ir3O11 with strong spin–orbit coupling and fractional valence was recently predicted to be a quantum spin liquid candidate at ambient conditions. Here, we systematically investigate the evolution of structural and electronic properties of La3Ir3O11 under high pressure. Electrical transport measurements reveal an abnormal insulating behavior rather than metallization above a critical pressure P c ∼ 38.7 GPa. Synchrotron x-ray diffraction (XRD) experiments indicate the stability of the pristine cubic KSbO3-type structure up to 73.1 GPa. Nevertheless, when the pressure gradually increases across P c, the bulk modulus gets enhanced and the pressure dependence of bond length d Ir – Ir undergoes a slope change. Consistent with the XRD data, detailed analyses of Raman spectra reveal an abnormal redshift of Raman mode and a change of Raman intensity around P c. Our results demonstrate that the pressure-induced insulating behavior in La3Ir3O11 can be assigned to the structural modification, such as the distortion of IrO6 octahedra. These findings will shed light on the emergent abnormal insulating behavior in other 5d iridates reported recently.

CdCr2S4 single crystal was reported by Hemberger et al. to be multiferroic with the evidences of relaxor ferroelectricity and colossal magnetocapacitance (CMC), but whether these effects are intrinsic is under debate. Recently, we reported a one-to-one correlation between CMC and colossal magnetoresistance (CMR) in CdCr2S4 polycrystalline samples, and argued that CMC could be explained by the superposition of the CMR and the Maxwell–Wagner effects. In this paper, we further examined the magnetic, dielectric, and electric transport properties of CdCr2S4 and CdCr1.8In0.2S4 single crystals before and after annealing in cadmium vapor. The CdCr2S4 single crystal sample has no relaxor ferroelectricity and CMC, and in contrast to the CdCr2S4 single crystal reported by Hemberger et al. , only the annealed CdCr1.8In0.2S4 displays CMC, but still does not exhibit the relaxor behavior. At the same time, it also shows CMR. All these results are in accordance with the results of our polycrystalline samples, and further confirm the resistive origin of the CMC in the CdCr2S4 system.

High-pressure experiments usually expect a hydrostatic condition, in which the physical properties of materials can be easily understood by theoretical simulations. Unfortunately, non-hydrostatic effect is inevitable in experiments due to the solidification of the pressure transmitting media under high pressure. Resultantly, non-hydrostaticity affects the accuracy of the experimental data and sometimes even leads to false phenomena. Since the non-hydrostatic effect is extrinsic, it is quite hard to analyze quantitatively. Here, we have conducted high pressure experiments on the layered BiCuXO (X = S and Se) single crystals and quantitatively analyzed their pronounced non-hydrostatic effect by high throughput first-principles calculations and experimental Raman spectra. Our experiments find that the BiCuXO single crystals sustain the tetragonal structure up to 55 GPa (maximum pressure in our experiment). However, their pressure-dependent Raman shift and electric resistance show anomalous behaviors. Through optimization of thousands of crystal structures in the high throughput first-principles calculations, we have obtained the evolution of the lattice constants under external pressures, which clearly substantiates the non-hydrostatical pressure exerted in BiCuXO crystals. Our work indicates that the high throughput first-principles calculations could be a handy method to investigate the non-hydrostatic effect on the structural and electronic properties of materials in high pressure experiments.

We present a high-pressure study of van der Waals ferromagnetic metal Fe3GeTe2 through electrical transport and Raman scattering measurements in diamond anvil cells at pressures up to 22.4GPa. Upon compression, the ferromagnetic transition temperature T c manifested by a kink in resistance curve decreases monotonically and becomes undiscernable around P c = 10GPa, indicative of suppression of the itinerant ferromagnetism. Meanwhile, by fitting the low temperature resistance to the Fermi liquid behavior of R = R 0 + AT 2, we found that R 0 shows a cusp-like anomaly and the coefficient A diverges around P c. These transport anomalies imply a tricritical point as commonly observed in itinerant ferromagnets under pressure. Unexpectedly, the Raman-active E 2g and A 1g modes soften remarkably after an initial weak hardening and the peak widths of both modes broaden evidently on approaching P c, followed by complete disappearance of both modes above this critical pressure. A possible underlying mechanism for such anomalous lattice softening near P c is discussed.

Tetradymite-type topological insulator Sn-doped $\mathrm{B}{\mathrm{i}}_{1.1}\mathrm{S}{\mathrm{b}}_{0.9}\mathrm{T}{\mathrm{e}}_{2}\mathrm{S}$ (Sn-BSTS), with a surface state Dirac point energy well isolated from the bulk valence and conduction bands, is an ideal platform for studying the topological transport phenomena. Here, we present high-pressure transport studies on single-crystal Sn-BSTS, combined with Raman scattering and synchrotron x-ray diffraction measurements. Over the studied pressure range of 0.7--37.2 GPa, three critical pressure points can be observed: (i) At $\ensuremath{\sim}9$ GPa, a pressure-induced topological insulator-to-metal transition is revealed due to closure of the bulk band gap, which is accompanied by changes in slope of the Raman frequencies and a minimum in $c$/$a$ within the pristine rhombohedral structure ($R\text{\ensuremath{-}}3m$); (ii) at $\ensuremath{\sim}13$ GPa, superconductivity is observed to emerge, along with the $R\text{\ensuremath{-}}3m$ to a $C2$/$c$ (monoclinic) structural transition; (iii) at $\ensuremath{\sim}24$ GPa, the superconducting transition onset temperature ${T}_{\mathrm{C}}$ reaches a maximum of $\ensuremath{\sim}12\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, accompanied by a second structural transition from the $C2$/$c$ to a body-centered cubic $Im\text{\ensuremath{-}}3m$ phase.