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The equiatomic metal-rich phosphide NbCrP shows a structural phase transition around 125 K. The structures of the high- and low-temperature modifications were refined from single crystal X-ray diffractometer data of an un-twinned crystal: TiNiSi type, Pnma, a = 619.80(2), b = 353.74(4), c = 735.24(6) pm, wR = 0.0706, 288 F 2 values, 20 variables at 240 K and P121/c1, a = 630.59(3), b = 739.64(4), c = 933.09(5) pm, β = 132.491(6)°, wR = 0.0531, 1007 F 2 values, 57 variables at 90 K. The structural phase transition is of a classical Peierls type. The equidistant chromium chain in HT-NbCrP (353.7 pm Cr–Cr) splits pairwise into shorter (315.2 pm) and longer (373.2 pm) Cr–Cr distances. This goes along with a strengthening of Cr–P bonding. The superstructure formation is discussed on the basis of a group–subgroup scheme. Electronic structure calculations show a lifting of band degeneracy. Protection of the non-symmorphic symmetry of space group Pnma is crucial for the phase transition. The estimated charge modulation is consistent with the interpretation as Peierls transition.

Cubic CeZn shows a structural phase transition under pressure, and it modifies the ground state from an antiferromagnetic (AFM) state to a ferromagnetic (FM) state. To investigate how the FM state terminates at a quantum phase transition, we measured the electrical resistivity under pressure for a single crystal CeZn. The transition temperature into the FM state decreases monotonously with increasing pressure, accompanied by the pronounced Kondo effect, but a drastic change in the field response occurs before the ordered phase terminates. This result suggests that the FM quantum critical point is avoided by the appearance of an AFM-like state., 5 pages, 3 figures

LaCrGe${}_{3}$ is a unique itinerant ferromagnet that exhibits an avoided ferromagnetic quantum critical point (QCP) under pressure. This occurs due to a change in the order of the phase transition as well as through a new high-pressure magnetic state, which is suggested either to be antiferromagnetic or short-range ferromagnetic. The NMR data taken here under pressure are consistent with the recently proposed short-range ferromagnetic order. Furthermore, the authors have discovered the persistent presence of three-dimensional ferromagnetic fluctuations even at pressures close to the putative QCP.

We performed $^{59}$Co nuclear magnetic and quadrupole resonance (NMR and NQR) measurements under pressure on a single-crystalline CeCoSi, which undergoes an unresolved phase transition at $T_0$. The NQR spectra clearly showed that the phase transition at $T_0$ is nonmagnetic, but any symmetry lowering at the Co site was not seen irrespective of the feature of second-order phase transition. By contrast, the NMR spectra were split by the induced magnetic field perpendicular to the external magnetic field. These results show that the phase below $T_0$ is not a simple paramagnetic state but is most likely electric multipolar ordered state of Ce $4f$ electrons. The development of the Kondo effect by applying pressure is thought to be crucial to stabilize this state and to show novel features beyond commonality of tetragonal Ce-based systems., 6 pages, 4 figures

We report the discovery of a first-order phase transition at around 125 K in NbCrP, which is a nonsymmorphic crystal with Pnma space group. From the resistivity, magnetic susceptibility, and nuclear magnetic resonance measurements using the crystals made by the Sn-flux method, the high-temperature (HT) phase is characterized to be metallic with a non-negligible magnetic anisotropy. The low-temperature (LT) phase is also found to be a nonmagnetic metallic state with a crystal of lower symmetry. In the LT phase, the spin susceptibility is reduced by ~30 % from that in the HT phase, suggesting that the phase transition is triggered by the electronic instability. The possible origin of the phase transition in NbCrP is discussed based on the electronic structure by comparing with those in other nonsymmorphic compounds RuP and RuAs., Comment: 9 pages, 9 Postscript figures

The connection between ferromagnetic (FM) fluctuations and superconductivity has been well established in FM superconductors UCoGe and URhGe. However, this connection has not been clarified in UGe2...

In conventional metals, modification of electron trajectories under magnetic field gives rise to a magnetoresistance that varies quadratically at low field, followed by a saturation at high field for closed orbits on the Fermi surface. Deviations from the conventional behaviour, for example, the observation of a linear magnetoresistance, or a non-saturating magnetoresistance, have been attributed to exotic electron scattering mechanisms. Recently, linear magnetoresistance has been observed in many Dirac materials, in which the electron–electron correlation is relatively weak. The strongly correlated helimagnet CrAs undergoes a quantum phase transition to a nonmagnetic superconductor under pressure. Here we observe, near the magnetic instability, a large and non-saturating quasilinear magnetoresistance from the upper critical field to 14 T at low temperatures. We show that the quasilinear magnetoresistance may arise from an intricate interplay between a nontrivial band crossing protected by nonsymmorphic crystal symmetry and strong magnetic fluctuations., The electronic structure of the helimagnet CrAs is unusual due to its nonsymmorphic crystal symmetry. Here, the authors observe quasilinear magnetoresistance close to a pressure-driven superconducting transition, which may arise from the interaction of the band structure and magnetic fluctuations.

We performed 27Al-NMR measurements for the CaBe2Ge2 type single crystalline LaPd2Al2 in the temperature range from 100 K to 5 K to investigate the origin of the structural phase transition. We found that the line profile of the 27Al-NMR spectrum does not change entirely on passing through the structural phase transition at T st . Meanwhile, the peak position of the central line slightly change ( ≈ 30 ppm) below 70 K, suggesting the orbital shift changes below T st . The present 27Al-NMR studies evidence that the local electronic state at Al site is hardly affected by the structural phase transition.

We report 73Ge-NMR measurement on the ferromagnetic superconductor UGe2 at ambient pressure. The observed NMR spectrum supports that the electric field gradient at three inequivalent Ge sites is correctly deduced by a LDA calculation. The temperature dependences of the nuclear spin lattice relaxation rate 1 / T 1 for H 0 ⊥ a (easy axis) and H 0 ∥ a were obtained for the oriented sample. The contrasting behavior in 1 / T 1 for H 0 ⊥ a and H 0 ∥ a reveals that the magnetic fluctuation of UGe2 is highly anisotropic.

We report NMR spectrum analysis for CrAs, which was recently reported to be superconducting under pressure. The NMR spectrum obtained by the powdered single crystals shows a typical powder pattern reproduced by the electric field gradient (EFG) parameters and isotropic Knight shift, indicating anisotropy of Knight shift is not remarkable in CrAs. For the oriented sample, the spectrum can be understood by considering that the crystals are aligned for H ∥ b . The temperature dependence of Knight shift was successfully obtained from NMR spectrum with large nuclear quadrupole interaction.

We have performed a susceptibility M / H and 11 B NMR measurements to investigate the static magnetic anisotropy of a single crystal UNi 4 B. The Knight shift 11 K and the hyperfine coupling constant A hf evaluated by 11 K - M / H plot show anisotropic behavior between H ∥ [ 11 2 ¯ 0 ] and H ∥ [ 0001 ] , reflecting the bulk susceptibility. The evaluated transferred term A tr of A hf for H ∥ [ 11 2 ¯ 0 ] is much larger than the one for H ∥ [ 0001 ] . The strong hybridization in the [0001]-plane due to a itinerant 5 f -electron is strongly associated with the unique magnetic structure in this compound.

In order to clarify unusual superconducting properties in a heavy fermion superconductor UBe13, we have carried out 9Be NMR measurements using a single crystal with T c ≅ 0.85 K . The NMR spectra under the magnetic field H = 3 T parallel to [111] crystal axis show no change between T c ( H = 3 T ) = 0.64 K and T a ( H = 3 T ) = 0.55 K . Below T a , however, the Knight shift for Be(II) decreased. The reduction of the Knight shift of Be(II) is amount to ∼ 0.01 % , which is much smaller than spin part of the Knight shift, K s ∼ 0.1 % estimated from Clogston Jaccarino plot. The origin of reduction of the Knight shift cannot be explained by spin singlet superconductivity.

The anisotropic changes in the electronic structure of a metal-to-insulator transition (MIT) material, RuAs, with two-step phase transition are reported by using polarized optical conductivity [$\sigma(\omega)$] spectra, angle-integrated photoelectron (PE) spectra, and band calculations based on local density approximation (LDA). Both the PE and $\sigma(\omega)$ spectra not only in the high-temperature (HT) phase but also in the low-temperature (LT) phase as well as the energy gap formation owing to the MIT were almost consistent with those derived from the LDA band calculations, so the fundamental electronic structure in the HT and LT phases can be explained without electron correlations. However, the electronic structure in the middle phase between the HT and LT phases has not been clarified. The polarized $\sigma(\omega)$ spectra revealed not only the anisotropic energy gap formation but also the anisotropic gap-opening temperature, i.e., the energy gap along the $c$ axis in the HT phase starts to open near the higher transition temperature, but that along the $b$ axis opens below the lower transition temperature. The finding suggests that the two-step MIT originates from the anisotropic energy gap formation., Comment: 7 pages, 7 figures

We report $^{75}\mathrm{As}$-NMR results for CrAs under pressure, which shows superconductivity adjoining a helimagnetically ordered state. We successfully evaluated the Knight shift from the spectrum, which is strongly affected by the quadrupole interaction. The Knight shift shows the remarkable feature that the uniform spin susceptibility increases toward low temperatures in the paramagnetic state. This is in sharp contrast to CrAs at ambient pressure, and also to cuprates and Fe pnictides, where antiferromagnetic correlations are dominant. Superconductivity emerges in CrAs under unique magnetic correlations, which probably originate in the three-dimensional zigzag structure of its nonsymmorphic symmetry.

Antiferromagnet Mn_{3}P with Neel temperature T_{N}=30 K is composed of Mn tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at ∼1.6 GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn_{3}P, which is most likely effected by the underlying frustration effect.

Author(s): Rana, K; Kotegawa, H; Ullah, RR; Harvey, JS; Bud'Ko, SL; Canfield, PC; Tou, H; Taufour, V; Furukawa, Y | Abstract: LaCrGe3 is an itinerant ferromagnet with a Curie temperature of TC=85 K and exhibits an avoided ferromagnetic quantum critical point under pressure through a modulated antiferromagnetic phase as well as tricritical wing structure in its temperature-pressure-magnetic field (T-p-H) phase diagram. In order to understand the static and dynamical magnetic properties of LaCrGe3, we carried out La139 nuclear magnetic resonance (NMR) measurements. Based on the analysis of NMR data, using the self-consistent-renormalization (SCR) theory, the spin fluctuations in the paramagnetic state are revealed to be isotropic ferromagnetic and three dimensional (3D) in nature. Moreover, the system is found to follow the generalized Rhodes-Wohlfarth relation which is expected in 3D itinerant ferromagnetic systems. As compared to other similar itinerant ferromagnets, the Cr 3d electrons and their spin fluctuations are characterized to have a relatively high degree of localization in real space.

We report resistivity measurements under pressure for Kondo-lattice ferromagnet CeRh$_6$Ge$_4$, and present that a quantum ferromagnetic (FM) phase transition is easily achieved. In most clean metallic ferromagnets, a quantum critical point (QCP) at zero field is avoided by changing the FM transition to a discontinuous transition or to an antiferromagnetic transition. In CeRh$_6$Ge$_4$, to the contrary, the Curie temperature of 2.5 K decreases continuously as increasing pressure without any clear signature that the transition changes to first order. The obvious non Fermi liquid behavior is observed in the vicinity of the quantum FM phase transition. The experimental data do not contradict a picture in which CeRh$_6$Ge$_4$ shows the FM QCP at zero field. Band structure calculation suggests the unusual electronic state of CeRh$_6$Ge$_4$ among Ce-based Kondo lattices. CeRh$_6$Ge$_4$ deserves further investigations and will be a key material to understand the matter of the FM QCP., Comment: 5 pages, 6 figures

We report on the first observation of the de Haas–van Alphen (dHvA) effect in CrAs under hydrostatic pressures of up to 2.2 GPa, exceeding the critical pressure Pc ∼ 0.7 GPa, where the antiferromag...

We have investigated the Fermi surface properties in the Pr-based heavy-fermion superconductor PrTi2Al20 and its reference compound LaTi2Al20 by means of the de Haas–van Alphen effect experiments and the band-structure calculation. The topology of Fermi surface in PrTi2Al20 is close to that of the reference compound LaTi2Al20, indicating a localized nature of 4f-electrons. Whereas the localized nature of 4f-electrons, we have confirmed a highly enhanced cyclotron effective mass up to 12 m0 (m0 is a rest mass of electron), which is enhanced about 5 times compared to that in LaTi2Al20.

195Pt-NMR measurements for H ∥ c in the vicinity of the upper critical field \(H_{\text{c2}}^{\| c}\) have been carried out on the heavy-fermion superconductor UPt3. The 195Pt NMR line does not cha...

Tetrahedrite Cu12Sb4S13 shows a metal–semiconductor transition (MST) at TMST = 85 K. We have studied the mechanism of the MST by measurements of Cu-NMR. Above TMST, the Cu-NMR spectrum consists of ...

We carried out 195Pt-NMR measurements for a single-crystal LaPt2Si2, which is expected to show the coexistence of a superconducting state and a charge density wave (CDW) state. LaPt2Si2 crystallize...

We have performed NMR measurements under pressure in UCoAl with a quantum critical endpoint of the metamagnetic transition from the paramagnetic phase to the ferromagnetic (FM) phase. 59Co-NMR sensitively detects the evolution of the internal field caused by applying the external field. The metamagnetic field H m increases with increasing pressure consistently with other experimental methods, accompanied by the suppression of the magnetization in the field-induced FM phase and the magnetization jump at H m . The loss of the NMR signal on approaching the QCEP indicates the development of the spin fluctuations.

We report a study of 139La(I=7/2) nuclear magnetic resonance (NMR) to investigate the structural phase transition in the two caged compounds LaIr2Zn20 and LaRu2Zn20 from microscopic viewpoints. The former compound shows a second-order structural phase transition around T s = 200 K whereas the latter one shows a first-order structural phase transition at T s = 150 K. For both compounds, quite narrow La-NMR lines of less that 10 kHz without any electric field gradient (EFG) at the La site were observed at temperatures above T s , indicating that the local symmetry at the La site holds a cubic symmetry. On the other hand, an EFG at La site appears at temperatures below T s , evidencing symmetry lowering occurs at the La site at temperatures below T s . At temperatures around T s , both the nuclear spin-lattice relaxation rate (1/T 1) and the nuclear spin-spin relaxation rate (1/T 2) show unusual enhancements associated with the slowing down of the EFG fluctuations. However, the temperature dependences of 1/T 1 T and 1/T 2 are different from the typical slowingdown phenomena of the EFG fluctuations due to the classical motional narrowing. The lowering of the local symmetry at the La site is ascribed to a freezing of the rattling motion.

We report a Cu NMR Knight shift K in a prototypical heavy-fermion system CeCu6 in the temperature range of 1.5 K–100 K at applied magnetic fields up to 15 T. With increasing magnetic field, the 63Cu NMR Knight shift for H‖[001] is suppressed drastically. The suppression of K with increasing field is consistent with the field dependence of the susceptibility. In order to explain this behavior, we adopted the Kondo resonance level model, where the thermodynamics at low temperatures are proportional to the density of states at the energy µH. The resonant model was found to correctly predict the suppression of the Knight shift with increasing magnetic field.

We performed 75As nuclear quadrupole resonance (NQR) measurements on single-crystalline Ru1−xRhxAs to study the relationship between the superconductivity observed in a limited Rh-substitution regi...

The single crystal of RuAs obtained by Bi-flux method shows obvious successive metal-insulator transitions at T_MI1~255 K and T_MI2~195$ K. The X-ray diffraction measurement reveals a formation of superlattice of 3x3x3 of the original unit cell below T_MI2, accompanied by a change of the crystal system from the orthorhombic structure to the monoclinic one. Simple dimerization of the Ru ions is nor seen in the ground state. The multiple As sites observed in nuclear quadrupole resonance (NQR) spectrum also demonstrate the formation of the superlattice in the ground state, which is clarified to be nonmagnetic. The divergence in 1/T_1 at T_MI1 shows that a symmetry lowering by the metal-insulator transition is accompanied by strong critical fluctuations of some degrees of freedom. Using the structural parameters in the insulating state, the first principle calculation reproduces successfully the reasonable size of nuclear quadrupole frequencies for the multiple As sites, ensuring the high validity of the structural parameters. The calculation also gives a remarkable suppression in the density of states (DOS) near the Fermi level, although the gap opening is insufficient. A coupled modulation of the calculated Ru d electron numbers and the crystal structure proposes a formation of charge density wave (CDW) in RuAs. Some lacking factors remain, but it shows that a lifting of degeneracy protected by the non-symmorphic symmetry through the superlattice formation is a key ingredient for the metal-insulator transition in RuAs., Comment: 10 pages, 10 figures

We report a 73Ge nuclear quadrupole resonance reinvestigation of the ferromagnetic (FM) superconductor UGe2 at ambient pressure. Careful measurement and analysis of the paramagnetic (PM) spectrum taking into account the calculated electric field gradient (EFG) resulted in modification of the previously reported site assignments for three inequivalent Ge sites. The crossover anomaly at Tx in the FM state is not clearly seen in the temperature dependence of the static internal field at the Ge site, whereas it appears in the nuclear spin–lattice relaxation rate, 1/T1. A remarkable site dependence of 1/T1 is observed among the inequivalent Ge sites, where the directions of the principal axes of the EFG are different. This result reveals that the magnetic fluctuation of UGe2 is highly anisotropic, which is consistent with the presence of Ising magnetic fluctuations in the PM state.

We have succeeded in observing the de Haas–van Alphen effect in PrOs 4 P 12 which shows no anomaly down to 50 mK in contrast to PrFe 4 P 12 and PrRu 4 P 12 . The Fermi surface (FS) topology is reasonably explained by the energy band structure calculation based on a full potential linearized augmented-plane-wave method within the local-density-approximation. Whereas the localized nature of 4 f -electrons, we have confirmed a highly enhanced cyclotron effective mass up to 18 m 0 in PrOs 4 P 12 , which is enhanced 3.8 times compared to that of LaOs 4 P 12 . No nesting property with q =(1,0,0) in the FS of PrOs 4 P 12 has been confirmed, which suggests both the 4 f -electron's contribution and the FS nesting property play the role for the phase transitions in PrFe 4 P 12 and PrRu 4 P 12 .

We report resistivity, nuclear quadrupole resonance (NQR), and magnetization measurements under high pressures in a novel heavy fermion compounds SmOs 4 Sb 12 . The resistivity and nuclear spin–lattice relaxation rate 1/ T 1 show the coherent behavior below a characteristic temperature T * = 20-25 K at ambient pressure. Nuclear spin–spin relaxation rate 1/ T 2 was found to show a peak of electrical origin around T * . Some charge fluctuation is considered to play an important role in the Kondo effect of SmOs 4 Sb 12 . On the other hand, the magnetization at low temperature does not increase under pressures, although the transition temperature increases. The NQR signals are strongly suppressed around the transition temperature and vanishes at low temperatures. These suggest that the ordered state in SmOs 4 Sb 12 is not simple ferromagnetism.

We report systematic Cu-NMR studies on five-layered cuprates from under-doped HgBa2Ca4Cu5O12+δ (Hg-1245(UD)) to slightly overdoped Tl-1245(OVD), and compare with optimally-doped Hg-1245(OPT). In the under-doped Hg-1245(UD), antiferromagnetism (AFM) has been found to take place at TN = 290 K, exhibiting a large antiferromagnetic moment of 0.67–0.69 μB at three inner planes (IP’s). These values are comparable to that reported for non-doped cuprates, suggesting that the IP’s may be in a nearly non-doped regime. Most surprisingly, the AFM order is also detected with MAFM(OP) = 0.1 μB even at two outer planes (OP’s) that are responsible for the onset of superconductivity (SC) with Tc = 72 K. The high-Tc SC at Tc = 72 K can uniformly coexist on a microscopic level with the AFM at OP’s. This is the first microscopic evidence for the uniformly mixed phase of AFM and SC on a single CuO2 plane. Although, the AFM/SC mixed CuO2 planes are significantly separated by three non-doped AFM layers, the onset of AFM does not prevent the occurrence of SC with the high value of Tc = 72 K.

Zero- and longitudinal-field muon-spin rotation (ZF-μSR and LF-μSR) measurements were carried out on a multi-layered HgBa 2 Ca 4 Cu 5 O y (Hg-1245) superconductor with T c of 108 K. With decreasing temperature, the observed ZF-μSR function changed from a Gaussian-type to an exponential-type below 60 K and zero field muon precession was also observed below 45 K. These μSR signals are attributed to the development of the antiferromagnetic ordering in inner CuO 2 planes with a low carrier concentration. These results seem to indicate clear evidence that antiferromagnetism microscopically coexists with superconductivity in the Hg-1245 superconductor below 60 K.

Pressure-induced superconductivity was recently discovered in the binary helimagnet CrAs. We report the results of measurements of nuclear quadrupole resonance for CrAs under pressure. In the vicinity of the critical pressure P(c) between the helimagnetic (HM) and paramagnetic (PM) phases, a phase separation is observed. The large internal field remaining in the phase-separated HM state indicates that the HM phase disappears through a strong first-order transition. This indicates the absence of a quantum critical point in CrAs; however, the nuclear spin-lattice relaxation rate 1/T(1) reveals that substantial magnetic fluctuations are present in the PM state. The absence of a coherence effect in 1/T(1) in the superconducting state provides evidence that CrAs is the first Cr-based unconventional superconductor.