Anomalous thermal expansion in a CuAl2-type superconductor CoZr2

In this work, we show that the CuAl2-type superconductor CoZr2 and alloyed systems exhibit anomalous thermal expansion in a wide temperature range. We performed neutron powder diffraction and X-ray powder diffraction on CoZr2 and observed remarkably anisotropic thermal expansion with a c-axis negative thermal expansion constant of {\alpha}c < -15 {\mu}K-1 in a wide temperature range of T = 50-573 K. With decreasing temperature, the lattice constant a decreases, while the lattice constant c continuously increases in CoZr2. The origin of the anisotropic shrinkage/expansion of the a-axis/c-axis by cooling is explained by the small change in the Co-Zr bond and the systematic decrease in the Zr-Co-Zr angle. Similar thermal expansion was observed in alloyed systems, (Fe,Co,Ni)Zr2 and (Fe,Co,Ni,Rh,Ir)Zr2, which suggests that the phenomenon is common feature in the TrZr2 system. We propose that zero-thermal expansion metals would be achieved by optimizing the contrasting thermal expansion of a-axis and c-axis in TrZr2.Comment: 17 pages, 5 figures, supplementary dat

Axis thermal expansion switching in transition-metal zirconides TrZr2 by tuning the c/a ratio

This study examines the temperature-dependent evolution of the lattice constants for various CuAl2-type compounds, including NiZr2, (Co,Rh,Ir)Zr2, (Fe,Co,Rh,Ir)Zr2, and (Co,Ni,Cu,Rh,Ir)Zr2, in the pursuit of negative or zero thermal expansion. Results reveal that NiZr2 has positive thermal expansion, while the other compounds exhibit uniaxial negative thermal expansion along the c-axis contraction. The study suggests that the c-axis thermal expansion can be controlled by manipulating the c/a ratio through Tr-site substitution, providing a design principle for achieving negative thermal expansion of the c-axis and potentially zero thermal expansion in a single compound in TrZr2 compounds.Comment: 13 pages, 4 figure

Tuning of Carrier Concentration and Superconductivity in High-Entropy-Alloy-Type Metal Telluride (AgSnPbBi)(1-x)/4InxTe

High-entropy-alloy-type (HEA-type) compound superconductors have been drawing much attention as a new class of exotic superconductors with local structural inhomogeneity. NaCl-type (Ag,In,Sn,Pb,Bi)Te is a typical HEA-type superconductor, but the carrier doping mechanism had been unclear. In this study, we synthesized (Ag,In,Sn,Pb,Bi)Te with various In concentration using high-pressure synthesis: the studied system is (AgSnPbBi)(1-x)/4InxTe (x = 0-0.4). Single-phase samples were obtained for x = 0-0.3. A semiconductor-like temperature dependence of resistivity was observed for x = 0, while superconductivity appeared for the In-doped samples. The highest transition temperature (Tc) was 3.0 K for x = 0.3. The Seebeck coefficient decreases with increase of x, which suggests that In3+ generates electron carriers in (AgSnPbBi)(1-x)/4InxTe. Tuning of carrier concentration and superconducting properties of (Ag,In,Sn,Pb,Bi)Te would be useful for further investigation of exotic superconductivity in the HEA-type compound.Comment: 11 pages, 4 figures, 1 tabl

Observation of nonvolatile magneto-thermal switching in superconductors

Applying a magnetic field to a solid changes its thermal-transport properties. Although such magneto-thermal-transport phenomena are usually small effects, giant magneto-thermal resistance has recently been observed in spintronic materials1,2 and superconductors3,4, opening up new possibilities in thermal management technologies. However, the thermal conductivity conventionally changes only when a magnetic field is applied due to the absence of nonvolatility, which limits potential applications of thermal switching devices5,6. Here, we report the observation of nonvolatile thermal switching that changes the thermal conductivity when a magnetic field is applied and retains the value even when the field is turned off. This unconventional magneto-thermal switching, surprisingly, arises in commercial Sn-Pb solders and is realized by phase-separated superconducting states and resultant nonuniform magnetic flux distributions. This result confirms the versatility of the observed phenomenon and aids the development of active solid-state thermal management devices.Comment: 33 pages, 5 figures & 9 extended data figure

Observation of nonvolatile magneto-thermal switching in superconductors

Abstract Applying a magnetic field to a solid changes its thermal-transport properties. Although such magneto-thermal-transport phenomena are usually small effects, giant magneto-thermal resistance has recently been observed in spintronic materials and superconductors, opening up new possibilities in thermal management technologies. However, the thermal conductivity conventionally changes only when a magnetic field is applied due to the absence of nonvolatility, which limits potential applications of thermal switching devices. Here, we report the observation of nonvolatile thermal switching that changes the electron thermal conductivity when a magnetic field is applied and retains the value even when the field is turned off. This unconventional magneto-thermal switching arises in commercial Sn-Pb solders and is realized by phase-separated superconducting states and resultant nonuniform magnetic flux distributions. This result confirms the versatility of the observed phenomenon and aids the development of active solid-state thermal management devices