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Main text This is the final report of CCT-K7.2021 key comparison of water-triple-point (TPW) cells. The primary objective of CCT-K7.2021 was a comparison of the participant national realizations of the TPW temperature. Each participant laboratory selected one of its TPW cells for use as a transfer cell, directly compared it against its national reference and delivered it to the pilot (NRC). The pilot then compared all transfer cells against two NRC reference cells and, finally, each participant laboratory retrieved its transfer cell and directly re-compared it against its TPW national reference. The initial measurements at the participant laboratories were started in April 2021. The final measurements at the participants' laboratories were completed in September 2022. The final report was approved by the CCT WG-KC in April 2023. The adaptive weighted average procedure was adopted to compute the Key Comparison Reference Value (KCRV) and the degrees of equivalence (DoEs) were reported for the participant laboratories. The maximum difference between two transfer cells was 92 μK with a standard deviation of 26 µK (almost a factor of two improvement compared to CCT-K7 results (2002-2004). The maximum difference between two TPW national realizations was 111 µK, with a standard deviation of 28 µK (improvement similar to the one reported for the transfer cells). While the pooled distribution of CCT-K7 results was bimodal, indicating the presence of two different sub-populations (the population of laboratories that referred to ocean water definition and the population of laboratories that did not consider it), the pooled distribution of CCT-K7.2021 results was no longer bimodal, but slightly asymmetrical, indicating a more harmonized approach to water isotopic corrections. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The authors construct a M-shaped double superconducting dome and reveal the correlation between the CDW order and superconductivity in the Kagome metal RbV${}_{3}$Sb${}_{5}$.

${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ is a newly discovered ${Z}_{2}$ topological kagome metal showing the coexistence of a charge-density-wave (CDW)-like order at ${T}^{*}=94\text{ }\text{ }\mathrm{K}$ and superconductivity (SC) at ${T}_{c}=2.5\text{ }\text{ }\mathrm{K}$ at ambient pressure. Here, we study the interplay between CDW and SC in ${\mathrm{CsV}}_{3}{\mathrm{Sb}}_{5}$ via measurements of resistivity, dc and ac magnetic susceptibility under various pressures up to 6.6 GPa. We find that the CDW transition decreases with pressure and experience a subtle modification at ${P}_{c1}\ensuremath{\approx}0.6--0.9\text{ }\text{ }\mathrm{GPa}$ before it vanishes completely at ${P}_{c2}\ensuremath{\approx}2\text{ }\text{ }\mathrm{GPa}$. Correspondingly, ${T}_{c}(P)$ displays an unusual $M$-shaped double dome with two maxima around ${P}_{c1}$ and ${P}_{c2}$, respectively, leading to a tripled enhancement of ${T}_{c}$ to about 8 K at 2 GPa. The obtained temperature-pressure phase diagram resembles those of unconventional superconductors, illustrating an intimated competition between CDW-like order and SC. The competition is found to be particularly strong for the intermediate pressure range ${P}_{c1}\ensuremath{\le}P\ensuremath{\le}{P}_{c2}$ as evidenced by the broad superconducting transition and reduced superconducting volume fraction. The modification of CDW order around ${P}_{c1}$ has been discussed based on the band structure calculations. This work not only demonstrates the potential to raise ${T}_{c}$ of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electron correlations in this novel family of topological kagome metals.

CsV_{3}Sb_{5} is a newly discovered Z_{2} topological kagome metal showing the coexistence of a charge-density-wave (CDW)-like order at T^{*}=94 K and superconductivity (SC) at T_{c}=2.5 K at ambient pressure. Here, we study the interplay between CDW and SC in CsV_{3}Sb_{5} via measurements of resistivity, dc and ac magnetic susceptibility under various pressures up to 6.6 GPa. We find that the CDW transition decreases with pressure and experience a subtle modification at P_{c1}≈0.6-0.9 GPa before it vanishes completely at P_{c2}≈2 GPa. Correspondingly, T_{c}(P) displays an unusual M-shaped double dome with two maxima around P_{c1} and P_{c2}, respectively, leading to a tripled enhancement of T_{c} to about 8 K at 2 GPa. The obtained temperature-pressure phase diagram resembles those of unconventional superconductors, illustrating an intimated competition between CDW-like order and SC. The competition is found to be particularly strong for the intermediate pressure range P_{c1}≤P≤P_{c2} as evidenced by the broad superconducting transition and reduced superconducting volume fraction. The modification of CDW order around P_{c1} has been discussed based on the band structure calculations. This work not only demonstrates the potential to raise T_{c} of the V-based kagome superconductors, but also offers more insights into the rich physics related to the electron correlations in this novel family of topological kagome metals.

In 2014, Joint United Nations Programme on HIV/AIDS (UNAIDS) put forward the goal of ending HIV epidemic by 2030 at the International AIDS Conference and proposed the strategic goal of achieving "three 90%" by 2020. This year is the closing year of this strategic goal, and all regions have begun to evaluate the progress of implementing the goal. This article discussed the progress of the implementation of the "three 90%", and scientifically interpreted the strategic goal. It is proposed that the goal is a relative and dynamic concept, and only if we sieze the opportunity to achieve the strategic goal and continuously enhance comprehensive prevention and control, can the HIV epidemic be better controlled.2014年，联合国艾滋病规划署（UNAIDS）在世界艾滋病大会上提出2030年终结艾滋病流行的目标并提出2020年实现“三个90%”的策略目标。今年是该策略目标的收官之年，各地开始对落实“三个90%”的进展进行评估。本文围绕“三个90%”实施进展情况展开论述，并对该策略目标进行科学解读，提出该目标是一个相对的、动态的概念，利用实现“三个90%”的契机，做到持续加强综合预防干预，才能更好地遏制艾滋病疫情流行和蔓延。.

The trilayer nickelate ${\mathrm{Nd}}_{4}{\mathrm{Ni}}_{3}{\mathrm{O}}_{10\ensuremath{-}\ensuremath{\delta}}$ was investigated by the measurements of x-ray diffraction, electrical resistivity, magnetic susceptibility, and heat capacity. The crystal structure data suggest a higher Ni valence in the inner perovskitelike layer. At ambient pressure the resistivity shows a jump at 162 K, indicating a metal-to-metal transition (MMT). The MMT is also characterized by a magnetic susceptibility drop, a sharp specific-heat peak, and an isotropic lattice contraction. Below $\ensuremath{\sim}50\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, a resistivity upturn with $logT$ dependence shows up, accompanied with negative thermal expansion. External hydrostatic pressure suppresses the resistivity jump progressively, coincident with the weakening of the $logT$ behavior. The low-temperature electronic specific-heat coefficient is extracted to be $\ensuremath{\sim}150\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mol}\text{\ensuremath{-}}{\mathrm{f}.\mathrm{u}.}^{\ensuremath{-}1}$, equivalent to $\ensuremath{\sim}50\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mol}\text{\ensuremath{-}}{\mathrm{Ni}}^{\ensuremath{-}1}$, indicating an unusual heavy-electron correlated state. The novel heavy-electron state as well as the logarithmic temperature dependence of resistivity is explained in terms of the ${\mathrm{Ni}}^{3+}$-centered Kondo effect in the inner layer of the ${({\mathrm{NdNiO}}_{3})}_{3}$ trilayers.

The magnetic Weyl semimetal $\mathrm{C}{\mathrm{o}}_{3}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{S}}_{2}$ exhibits large anomalous Hall effect (AHE) due to its nontrivial band topology with enhanced Berry curvature. Here we investigate the pressure effect on the AHE of $\mathrm{C}{\mathrm{o}}_{3}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{S}}_{2}$ up to 12 GPa with a palm cubic anvil cell apparatus and first-principles calculations simulation. We find that both the ferromagnetic transition temperature and the AHE are suppressed monotonically upon the application of high pressure. Data analyses revealed that in the investigated pressure range the intrinsic mechanism due to Berry curvature dominates the AHE as reflected by the validation of ${\ensuremath{\rho}}_{xy}^{A}\ensuremath{\propto}{\ensuremath{\rho}}_{xx}^{2}$. However, both the anomalous Hall conductivity and anomalous Hall angle are reduced gradually into the regime for conventional ferromagnetic metals with trivial band topology. Combined with theoretical calculations, our results indicate that the distance between Weyl points with opposite chirality in $\mathrm{C}{\mathrm{o}}_{3}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{S}}_{2}$ is substantially reduced accompanying the suppression of ferromagnetism by pressure, thus providing an experimental route to tune the AHE of magnetic Weyl semimetals via modifying the nontrivial band topology.

To explore the spatio-temporal characteristics ofThe number of snail habitats showed a tendency towards a rise in the study area from 2012 to 2017, and snail habitats were predominantly distributed in the 1 000 m long buffer zone of the Danyang-Jintan-Liyang Canal, notably along the Jiuqu River at the junction between the Beijing-Hangzhou Grand Canal and the Danyang-Jintan-Liyang Canal. The distribution of snail habitats appeared spatial autocorrelations in 2014, 2016 and 2017, and the hotspot areas were mainly identified at the junction between the Danyang-Jintan-Liyang Canal and the Beijing-Hangzhou Grand Canal. In addition, the overall distribution of snail habitats was located in the northeastern-southwestern part of the study aera, and gradually shifted to the southern and northern parts with the time.The spatial distribution of

The $n$-type ${\text{HgCr}}_{2}{\mathrm{Se}}_{4}$ exhibits a sharp semiconductor-to-metal transition (SMT) in resistivity accompanying the ferromagnetic order at ${T}_{C}=106\text{ }\text{ }\mathrm{K}$. Here, we investigate the effects of pressure and magnetic field on the concomitant SMT and ferromagnetic order by measuring resistivity, dc and ac magnetic susceptibility, as well as single-crystal neutron diffraction under various pressures up to 8 GPa and magnetic fields up to 8 T. Our results demonstrate that the ferromagnetic metallic ground state of $n$-type ${\text{HgCr}}_{2}{\mathrm{Se}}_{4}$ is destabilized and gradually replaced by an antiferromagnetic, most likely a spiral magnetic, and insulating ground state upon the application of high pressure. On the other hand, the application of external magnetic fields can restore the ferromagnetic metallic state again at high pressures, resulting in a colossal magnetoresistance (CMR) as high as $\ensuremath{\sim}\text{ }3\ifmmode\times\else\texttimes\fi{}{10}^{11}%$ under 5 T and 2 K at 4 GPa. The present study demonstrates that $n$-type ${\text{HgCr}}_{2}{\mathrm{Se}}_{4}$ is located at a peculiar critical point where the balance of competition between ferromagnetic and antiferromagnetic interactions can be easily tipped by external stimuli, providing a new platform for achieving CMR in a single-valent system.

We have synthesized the high-pressure form of $\mathrm{CrS}{\mathrm{b}}_{2}$ with $\mathrm{CuA}{\mathrm{l}}_{2}$-type structure under 7 GPa and 700 \ifmmode^\circ\else\textdegree\fi{}C, and characterized its structural, transport, and magnetic properties by a suite of measurement techniques over a broad range of temperature, magnetic field, and pressure. In addition to previously reported ferromagnetic (FM) transition at ${T}_{\mathrm{C}}\ensuremath{\approx}160$ K, we discover another antiferromagnetic spin-density-wave (SDW) transition at ${T}_{\mathrm{s}}\ensuremath{\approx}90$ K, which is characterized by FM sheets of spins in the $ab$ plane that vary along the $c$ axis as determined by neutron powered diffraction. Pronounced anomalies around these two magnetic transitions are visible only in the lattice parameter $c$, signaling a strong spin-lattice coupling along the -Cr-Cr-Cr- infinite linear chain. We find that the application of magnetic field can suppress the SDW phase and stabilize the FM state down to the lowest temperature above ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}}\ensuremath{\approx}3$ T, around which a peculiar non-Fermi-liquid behavior with reduced effective mass emerges. On the other hand, the application of high pressure induces complex evolution of the magnetic states, i.e., the FM order is lowered while the SDW order is enhanced quickly until they merge together into a single antiferromagnetic transition, which is suppressed completely at ${P}_{\mathrm{c}}\ensuremath{\approx}9$ GPa. We observe near ${P}_{\mathrm{c}}$ non-Fermi-liquid behavior and enhancement of effective mass, which indicates the possible occurrence of magnetic quantum critical point. No superconductivity was observed down to 2 K around ${P}_{\mathrm{c}}$.

The n-type HgCr_{2}Se_{4} exhibits a sharp semiconductor-to-metal transition (SMT) in resistivity accompanying the ferromagnetic order at T_{C}=106 K. Here, we investigate the effects of pressure and magnetic field on the concomitant SMT and ferromagnetic order by measuring resistivity, dc and ac magnetic susceptibility, as well as single-crystal neutron diffraction under various pressures up to 8 GPa and magnetic fields up to 8 T. Our results demonstrate that the ferromagnetic metallic ground state of n-type HgCr_{2}Se_{4} is destabilized and gradually replaced by an antiferromagnetic, most likely a spiral magnetic, and insulating ground state upon the application of high pressure. On the other hand, the application of external magnetic fields can restore the ferromagnetic metallic state again at high pressures, resulting in a colossal magnetoresistance (CMR) as high as ∼ 3×10^{11}% under 5 T and 2 K at 4 GPa. The present study demonstrates that n-type HgCr_{2}Se_{4} is located at a peculiar critical point where the balance of competition between ferromagnetic and antiferromagnetic interactions can be easily tipped by external stimuli, providing a new platform for achieving CMR in a single-valent system.

RbGd

The cubic pyrochlore $\mathrm{C}{\mathrm{d}}_{2}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}$ develops a metalliclike state below the antiferromagnetic transition at ${T}_{\mathrm{N}}\ensuremath{\approx}90\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, in contrast to the sharp transition to an insulating state below ${T}_{\mathrm{N}}$ of the $5d$-analog ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$. We have synthesized polycrystalline $\mathrm{C}{\mathrm{d}}_{2}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}$ under high pressure, and investigated the responses of its electronic behavior to hydrostatic pressure and isovalent substitutions of ${\mathrm{Ca}}^{2+}$ for ${\mathrm{Cd}}^{2+}$. Three characteristic anomalies are identified in the electrical transport and magnetic properties of $\mathrm{C}{\mathrm{d}}_{2}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}$, signaling an intimate correlation between charge and spin degrees of freedom. Interestingly, we found that the metalliclike state of $\mathrm{C}{\mathrm{d}}_{2}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}$ below ${T}_{\mathrm{N}}$ is very fragile and can be suppressed by a small hydrostatic pressure of $\ensuremath{\le}1\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ or substitution of 5--10% ${\mathrm{Ca}}^{2+}$ for ${\mathrm{Cd}}^{2+}$, resulting in a resistivity behavior similar to that of ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$. In addition, the resultant insulating state below ${T}_{\mathrm{N}}$ is very robust against pressure, and the resistivity evolves gradually into two distinct activated regions under higher pressures. We constructed a temperature-pressure phase diagram for $\mathrm{C}{\mathrm{d}}_{2}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}$ and discussed its peculiar metalliclike state in terms of the electronic itinerancy/localization dichotomy via side-by-side comparisons with the related compounds ${A}_{2}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}(A=\mathrm{Ca},\mathrm{Hg})$ and ${\mathrm{Cd}}_{2}{\mathrm{Os}}_{2}{\mathrm{O}}_{7}$. Our results demonstrate that these cubic $4d/5d$ pyrochlore oxides offer an important paradigm for studying the exotic physics of correlated electrons on the border of (de)localization in the presence of strong geometrical frustration.

As infrared remote sensors are very important parts of Earth observation satellites, they must be calibrated based on the radiance temperature of a blackbody in a vacuum chamber prior to launch. The uncertainty of such temperature is thus an essential component of the sensors’ uncertainty. This paper describes the vacuum radiance-temperature standard facility (VRTSF) at the National Institute of Metrology of China, which will serve to calibrate infrared remote sensors on Chinese meteorological satellites. The VRTSF can be used to calibrate vacuum blackbody radiance temperature, including those used to calibrate infrared remote sensors. The components of the VRTSF are described in this paper, including the VMTBB, the LNBB, the FTIR spectrometer, the reduced-background optical system, the vacuum chamber used to calibrate customers’ blackbody, the vacuum-pumping system and the liquid-nitrogen-support system. The experimental methods and results are expounded. The uncertainty of the radiance temperature of VMTBB is 0.026 °C at 30 °C over 10 μm.

Based on the calibration requirements of vacuum low background aerospace infrared remote sensing radiance temperature, a high-precision vacuum blackbody (H500 type) is developed for the temperature range from − 93 °C to + 220 °C at the National Institute of Metrology, China. In this paper, the structure and the temperature control system of H500 are introduced, and its performance, such as heating rate and stabilization of temperature control, is tested under the vacuum and low-background condition (liquid-nitrogen-cooled shroud). At room temperature and atmospheric environment, the major technical parameters of this blackbody, such as emissivity and uniformity, are measured. The measurement principle of blackbody emissivity is based on the control of surrounding radiation. Temperature uniformity at the cavity bottom is measured using a standard infrared radiation thermometer. When the heating rate is 1 °C min−1, the time required for the temperature to stabilize is less than 50 min, and within 10 min, the variation in temperature is less than 0.01 °C. The emissivity value of the blackbody is higher than 0.996. Temperature uniformity at the bottom of the blackbody cavity is less than 0.03 °C. The uncertainty is less than 0.1 °C (k = 2) over the temperature range from − 93 °C to + 67 °C.

A well-known feature of the ${\mathrm{CaFe}}_{2}{\mathrm{As}}_{2}$-based superconductors is the pressure-induced collapsed tetragonal phase that is commonly ascribed to the formation of an interlayer As--As bond. Using detailed x-ray scattering and spectroscopy, we find that Rh-doped ${\mathrm{Ca}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ does not undergo a first-order phase transition and that local Fe moments persist despite the formation of interlayer As--As bonds. Our density functional theory calculations reveal that the Fe--As bond geometry is critical for stabilizing magnetism and the pressure-induced drop in the $c$ lattice parameter observed in pure ${\mathrm{CaFe}}_{2}{\mathrm{As}}_{2}$ is mostly due to a constriction within the FeAs planes. The collapsed tetragonal phase emerges when covalent bonding of strongly hybridized Fe $3d$ and As $4p$ states completely wins out over their exchange splitting. Thus the collapsed tetragonal phase is properly understood as a strong covalent phase that is fully nonmagnetic with the As--As bond forming as a by-product.

We report a high-pressure study on the heavily electron doped $\mathrm{L}{\mathrm{i}}_{0.36}{(\mathrm{N}{\mathrm{H}}_{3})}_{y}\mathrm{F}{\mathrm{e}}_{2}\mathrm{S}{\mathrm{e}}_{2}$ single crystal by using a cubic anvil cell apparatus. The superconducting transition temperature ${T}_{c}\ensuremath{\approx}44\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at ambient pressure is first suppressed to below 20 K upon increasing pressure to ${P}_{c}\ensuremath{\approx}2\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, above which the pressure dependence of ${T}_{c}(P)$ reverses and ${T}_{c}$ increases steadily to ca. 55 K at 11 GPa. These results thus evidence a pressure-induced second high-${T}_{c}$ superconducting (SC-II) phase in $\mathrm{L}{\mathrm{i}}_{0.36}{(\mathrm{N}{\mathrm{H}}_{3})}_{y}\mathrm{F}{\mathrm{e}}_{2}\mathrm{S}{\mathrm{e}}_{2}$ with the highest ${T}_{c}^{\mathrm{max}}\ensuremath{\approx}55\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ among the FeSe-based bulk materials. Hall data confirms that in the emergent SC-II phase the dominant electron-type carrier density undergoes a fourfold enhancement and tracks the same trend as ${T}_{c}(P)$. Interestingly, we find a nearly parallel scaling behavior between ${T}_{c}$ and the inverse Hall coefficient for the SC-II phases of both $\mathrm{L}{\mathrm{i}}_{0.36}{(\mathrm{N}{\mathrm{H}}_{3})}_{y}\mathrm{F}{\mathrm{e}}_{2}\mathrm{S}{\mathrm{e}}_{2}$ and (Li,Fe)OHFeSe. The present study demonstrates that high pressure offers a distinctive means to further raise the maximum ${T}_{c}$ of heavily electron doped FeSe-based materials by increasing the effective charge-carrier concentration via a possible Fermi-surface reconstruction at ${P}_{c}$.

The precise transfer matrix method is going to be used to solve a p system of linear ordinary differential equations. The complete problem is extended by adding index calculation involved. It is chosen an index calculation scheme to obtain transfer expressions. A recurrence strategy is used in these equations and permits one to relate different points in the domain where boundary equations are defined. Finally a p algebraic system of transfer matrix equations is noted and solved. To show the efficiency and accuracy, the method is applied to determine the structural behavior of a bending beam with different supports and to solve a differential equation of second degree with different boundary conditions.This article was retracted because it was an unauthorized reproduction of a previously published article in another journal.

K

We theoretically propose that the single-crystal formed TaS is a new type of topological metal, hosting ring-shaped gapless nodal lines and triply degenerate points (TDPs) in the absence of spin-orbit coupling (SOC). In the presence of SOC, each TDP splits into four TDPs along the high-symmetric line in momentum space, and one of the nodal rings remains closed due to the protection of the mirror reflection symmetry, while another nodal ring is fully gapped and transforms into six pairs of Weyl points (WPs) carrying opposite chirality. The electronic structures of the projected surfaces are also discussed, the unique Fermi arcs are observed, and the chirality remains or vanishes depending on the projection directions. On the (010) projected surface, one may observe a Lifshitz transition. The new type of topological metal TaS is stable and experimentally achievable, and the coexistence of topological nodal lines, WPs, and TDPs in TaS makes it a potential candidate to study the interplay between different types of topological fermions.

Receiving voluntary counseling and testing in the urban area of Chongqing and willing to participate in the interview by oral informed consent; male and self-described as MSM. The content of the interview included basic information, sexual orientation, sexual role, the main place of making friends, the main place of sexual behavior, a long-term experience in other provinces and drug abuse.

Miniature Ga and Ga–In alloy fixed points as temperature standards are developed at National Institute of Metrology, China for the in situ calibration of temperature sensors. A quasi-adiabatic vacuum measurement system is constructed to study the phase-change plateaus of the fixed points. The system comprises a high-stability bath, a quasi-adiabatic vacuum chamber and a temperature control and measurement system. The melting plateau of the Ga fixed point is longer than 2 h at 0.008 W. The standard deviation of the melting temperature of the Ga and Ga–In alloy fixed points is better than 2 mK. The results suggest that the melting temperature of the Ga or Ga–In alloy fixed points is linearly related with the heating power.

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (${T}_{c}$). However, the absence of hole pockets near the Fermi level of the iron-selenide (FeSe) derived high-${T}_{c}$ superconductors raises a fundamental question of whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in the high-${T}_{c}$ phase induced by pressure in bulk FeSe from magnetotransport measurements and first-principles calculations. With increasing pressure, the low-${T}_{c}$ superconducting phase transforms into the high-${T}_{c}$ phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstrating dominant hole carriers in contrast to other FeSe-derived high-${T}_{c}$ systems. Moreover, the Hall coefficient is enlarged and the magnetoresistance exhibits anomalous scaling behaviors, evidencing strongly enhanced interband spin fluctuations in the high-${T}_{c}$ phase. These results in FeSe highlight similarities with high-${T}_{c}$ phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.

We report improvements to our previous (Zhang et al 2011 Int. J. Thermophys. 32 1297) determination of the Boltzmann constant kB using a single 80 mm long cylindrical cavity. In this work, the shape of the gas-filled resonant cavity is closer to that of a perfect cylinder and the thermometry has been improved. We used two different grades of argon, each with measured relative isotopic abundances, and we used two different methods of supporting the resonator. The measurements with each gas and with each configuration were repeated several times for a total of 14 runs. We improved the analysis of the acoustic data by accounting for certain second-order perturbations to the frequencies from the thermo-viscous boundary layer. The weighted average of the data yielded kB = 1.380 6476 × 10−23 J K−1 with a relative standard uncertainty ur(kB) = 3.7 × 10−6. This result differs, fractionally, by (−0.9 ± 3.7) × 10−6 from the value recommended by CODATA in 2010. In this work, the largest component of the relative uncertainty resulted from inconsistent values of kB determined with the various acoustic modes; it is 2.9 × 10−6. In our previous work, this component was 7.6 × 10−6.

The importance of electron-hole interband interactions is widely acknowledged for iron-pnictide superconductors with high transition temperatures (T_{c}). However, the absence of hole pockets near the Fermi level of the iron-selenide (FeSe) derived high-T_{c} superconductors raises a fundamental question of whether iron pnictides and chalcogenides have different pairing mechanisms. Here, we study the properties of electronic structure in the high-T_{c} phase induced by pressure in bulk FeSe from magnetotransport measurements and first-principles calculations. With increasing pressure, the low-T_{c} superconducting phase transforms into the high-T_{c} phase, where we find the normal-state Hall resistivity changes sign from negative to positive, demonstrating dominant hole carriers in contrast to other FeSe-derived high-T_{c} systems. Moreover, the Hall coefficient is enlarged and the magnetoresistance exhibits anomalous scaling behaviors, evidencing strongly enhanced interband spin fluctuations in the high-T_{c} phase. These results in FeSe highlight similarities with high-T_{c} phases of iron pnictides, constituting a step toward a unified understanding of iron-based superconductivity.

Prior to the superconducting transition at ${T}_{\mathrm{c}}\ensuremath{\approx}2.3\phantom{\rule{4pt}{0ex}}\mathrm{K}, \mathrm{M}{\mathrm{o}}_{3}\mathrm{S}{\mathrm{b}}_{7}$ undergoes a symmetry-lowering, cubic-to-tetragonal structural transition at ${T}_{\mathrm{s}}=\phantom{\rule{0.16em}{0ex}}53\phantom{\rule{4pt}{0ex}}\mathrm{K}$. We have monitored the pressure dependence of these two transitions by measuring the resistivity of $\mathrm{M}{\mathrm{o}}_{3}\mathrm{S}{\mathrm{b}}_{7}$ single crystals under various hydrostatic pressures up to 15 GPa. The application of external pressure enhances ${T}_{\mathrm{c}}$ but suppresses ${T}_{\mathrm{s}}$ until ${P}_{\mathrm{c}}\ensuremath{\approx}10\phantom{\rule{4pt}{0ex}}\mathrm{GPa}$, above which a pressure-induced first-order structural transition takes place and is manifested by the phase coexistence in the pressure range $8\ensuremath{\le}P\ensuremath{\le}12\phantom{\rule{4pt}{0ex}}\mathrm{GPa}$. The cubic phase above 12 GPa is also found to be superconducting with a higher ${T}_{\mathrm{c}}\ensuremath{\approx}6\phantom{\rule{4pt}{0ex}}\mathrm{K}$ that decreases slightly with further increasing pressure. The variations with pressure of ${T}_{\mathrm{c}}$ and ${T}_{\mathrm{s}}$ satisfy the Bilbro-McMillan equation, i.e. ${{T}_{\mathrm{c}}}^{n}{{T}_{\mathrm{s}}}^{1\ensuremath{-}n}=$ constant, thus suggesting the competition of superconductivity with the structural transition that has been proposed to be accompanied with a spin-gap formation at ${T}_{\mathrm{s}}$. Our first-principles calculations suggest the importance of magnetism that competes with the superconductivity in $\mathrm{M}{\mathrm{o}}_{3}\mathrm{S}{\mathrm{b}}_{7}$.