Pressure-induced Superconductivity Research Articles

Pressure-induced nontrivial Z2 band topology and superconductivity in the transition metal chalcogenide Ta2Ni3Te5

The unique electronic and crystal structures driven by external pressure in transition metal chalcogenides (TMCs) can host emergent quantum states. Here we report pressure-induced metallization, nontrivial ${Z}_{2}$ band topology, and superconductivity in TMC ${\mathrm{Ta}}_{2}{\mathrm{Ni}}_{3}{\mathrm{Te}}_{5}$. Our electrical transport measurements show that the metallization emerges at 3.3 GPa, followed by appearance of the superconductivity at ${P}_{\mathrm{c}}=21.3\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ with ${T}_{\mathrm{c}}\ensuremath{\sim}0.4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Room-temperature synchrotron x-ray-diffraction experiments demonstrate the stability of the pristine orthorhombic structure upon compression. Our first-principles calculations further reveal a topological phase transition (from ${Z}_{2}=0$ to ${Z}_{2}=1$), which occurs after ${\mathrm{Ta}}_{2}{\mathrm{Ni}}_{3}{\mathrm{Te}}_{5}$ is turned into an electron-hole compensated semimetal by pressure. The pressure-induced superconductivity at ${P}_{\mathrm{c}}$ could be attributed to the abruptly enhanced density of states at the Fermi level. These findings demonstrate that ${\mathrm{Ta}}_{2}{\mathrm{Ni}}_{3}{\mathrm{Te}}_{5}$ is a new platform for realizing exotic quantum phenomena in TMCs as well as exploring the interplay between topological property and superconductivity.

Pressure-induced stability and superconductivity in LuH12 polyhydrides.

The phase stability and superconductivity of lutetium polyhydrides under pressure were systematically explored via particle swarm optimization. Several lutetium hydrides, such as LuH, LuH3, LuH4, LuH6, LuH8, and LuH12, were found to be dynamically and thermodynamically stable. Combined with the electronic properties, there are a large number of H-s states and low density of Lu-f states at the Fermi level, leading to superconductivity. The phonon spectrum and electron-phonon coupling interaction are considered to calculate the superconducting critical temperature (Tc) of stable lutetium hydrides at high pressure. The new predicted cubic LuH12 has the highest Tc value of 187.2 K at 400 GPa in all the stable LuHn compounds, which was estimated by directly solving the Eliashberg equation. The calculated results provide insights into the design of new superconducting hydrides under pressure.

Pressure-induced high-temperature superconductivity in ternary Y-Zr-H compounds.

Compressed hydrogen-rich compounds have received extensive attention as appealing contenders for superconductors. Here, we found several stable hydrides YZrH6, YZrH8, YZr3H16 and YZrH18, and a series of metastable clathrate hexahydrides in the systematic investigation of Y-Zr-H ternary hydrides under pressure. Electron-phonon coupling calculations indicate that they all exhibit high temperature superconductivity and perform better than the binary Zr-H system. YZrH6 can maintain dynamic stability down to ambient pressure and keep a critical temperature (Tc) of 16 K. The stable YZrH18 and metastable Y3ZrH24 with high hydrogen content exhibit high Tc of 156 K and 185 K at 200 GPa, respectively. Further analysis shows that the phonon modes associated with H atoms contribute significantly to the electron-phonon coupling. The hydrogen content and the stoichiometric ratio of Y and Zr closely affect the density of states at the Fermi level, thereby affecting the superconductivity. Our work presents an important step toward understanding the superconductivity and stability of transition metal ternary hydrides.

Pressure-induced superconductivity of Ac-B-H hydrides.

The search for room-temperature superconductors among high-pressure hydrides is a hot research topic. In this study, the structures, stabilities and superconducting properties of ternary Ac-B-H hydrides were studied using a genetic algorithm (GA) combined with density functional theory (DFT) calculations. It was shown that the R3̄m-AcBH8 and I4/mmm-AcB2H8 structures were thermodynamically and dynamically stable above 70 and 125 GPa, respectively. In the R3̄m-AcBH8 structure, the BH6 unit and the dispersed H atoms were bonded to form a corrugated structure. The I4/mmm-AcB2H8 structure contained a cage and the Ac atom located at the cage center. The calculations of the electron-phonon coupling showed that the R3̄m-AcBH8 and I4/mmm-AcB2H8 structures had Tc values of 140 K (70 GPa) and 99 K (125 GPa), respectively. The analyses of the phonon dispersion curves revealed that electron-phonon coupling was closely related to the vibrations of the B-H bonds.

Flipping of antiferromagnetic to superconducting states in pressurized quasi-one-dimensional manganese-based compounds

One of the universal features of unconventional superconductors is that the superconducting (SC) state is developed in the proximity of an antiferromagnetic (AFM) state. Unified understanding the interplay between these two states in different superconducting systems is one of the key issues to uncover the underlying physics of unconventional SC mechanism. Here, we report a pressure-induced superconductivity in the quasi-one-dimensional $\mathrm{Cs}{\mathrm{Mn}}_{6}{\mathrm{Bi}}_{5}$ compound that bears an AFM state at ambient pressure. The SC state appears at the critical pressure $({P}_{c})$ of $\ensuremath{\sim}12$ GPa and stabilizes up to $\ensuremath{\sim}27$ GPa. The high-pressure x-ray-diffraction measurements on $\mathrm{Cs}{\mathrm{Mn}}_{6}{\mathrm{Bi}}_{5}$ indicate that no structural phase transition occurs at the ${P}_{c}$, indicating that the AFM-SC transition is electronic in origin. By comparing the previous results of $A{\mathrm{Mn}}_{6}{\mathrm{Bi}}_{5}$ ($A=\mathrm{K}$, Rb), we identify that all members of the family possess the genetic flipping behavior of AFM-SC states at almost the same ${P}_{c}$, though their ambient-pressure unit-cell volumes vary quite differently. Our theoretical calculations suggest that the pressure-induced changes of partial density of state contributed by the ${d}_{yz}$ and ${d}_{xz}/{d}_{{z}^{2}}$ orbital electrons near Fermi energy may be associated with the origin of the flipping. These results provide a diverse picture of the connection between the AFM and SC states in the $3d--$ transition-metal compounds.

Pressure-Induced Superconductivity in PdTeI with Quasi-One-Dimensional PdTe Chains

The quasi-one-dimensional material PdTeI exhibits unusual electronic transport properties at ambient pressure. Here, we systematically investigate both the structural and electronic responses of PdTeI to external pressure, through a combination of electrical transport, synchrotron X-ray diffraction (XRD), and Raman spectroscopy measurements. The charge density wave (CDW) order in PdTeI is fragile and the transition temperature TCDW decreases rapidly with the application of external pressure. The resistivity hump is indiscernible when the pressure is increased to ~1 GPa. Upon further compression, the resistivity dropping is observed approximately ~15 GPa and zero resistance is established above ~20 GPa, suggesting the occurrence of superconductivity. Combined XRD and Raman data evidence that the emergence of superconductivity is accompanied by a pressure-induced amorphization of PdTeI.

Superconducting Behavior of BaTi2(Sb1–yBiy)2O under Pressure

The crystal structure and superconducting properties of a new type of titanium-pnictide superconductor, BaTi2(Sb1-yBiy)2O (y = 0.2, 0.5, and 0.8), are comprehensively investigated over a wide pressure range to elucidate the effect of substituting Bi for Sb on the superconducting behavior. The behavior of superconducting properties under pressure changes drastically with y, as expected from the double-dome Tc-y phase diagram obtained at ambient pressure. In this study, three BaTi2(Sb1-yBiy)2O samples (y = 0.2, 0.5, and 0.8) are considered, which correspond to the first superconducting dome, nonsuperconducting part, and second superconducting dome, respectively, in the Tc-y phase diagram. The crystal of BaTi2(Sb1-yBiy)2O with y = 0.2 shows a clear collapse transition, i.e., a drastic shrinkage of the lattice constant c at ca. 5 GPa. Strictly speaking, the collapsed crystal phase coexists with the noncollapsed phase above 5 GPa. On the other hand, BaTi2(Sb1-yBiy)2O with y = 0.8 shows a continuous change in the crystal lattice with pressure, i.e., no collapse transitions. The pressure dependence of Tc for BaTi2(Sb1-yBiy)2O with y = 0.2 shows a drastic increase in Tc at approximately 5 GPa, where the collapse transition occurs, indicating a clear pressure-induced superconducting phase transition related to the collapse transition. The value of Tc for BaTi2(Sb1-yBiy)2O with y = 0.8 increases slightly up to ∼2 GPa and is almost constant at 2-13 GPa. It is found that the superconducting behavior under pressure can be unambiguously classified by y based on the double-dome Tc-y phase diagram, indicative of distinguishable superconducting features at different y values. In this study, we comprehensively discuss the superconducting properties of the exotic material, BaTi2(Sb1-yBiy)2O, with a double-dome Tc-y phase diagram.

Pressure-Induced Electronic Topological Transition and Superconductivity in Topological Insulator Bi2Te2.1Se0.9.

One approach to discovering topological superconductors is establishing superconductivity based on well-identified topological insulators. However, the coexistence of superconductivity and a topological state is always arcane. In this paper, we report how pressure tunes the crystal structure, electronic structure, and superconductivity in topological insulator Bi2Te2.1Se0.9. At ∼2.5 GPa, the abnormal changes in c/a and the full width at half-maximum of the A1g1 mode indicate the occurrence of an electronic topological transition. The pressure-induced superconductivity in Bi2Te2.1Se0.9 pinned with an electronic topological transition presents at 2.4 GPa, which is far below the structural phase transition pressure of 8.4 GPa. These results suggest that the appearance of an electronic topological transition is closely correlated with superconductivity in the initial phase, where the topological surface state persists. Our work clarifies the complex electronic structure of Bi2Te2.1Se0.9 and sheds light on the mechanism for superconductivity in topological insulators.

Frustrated Magnetic Interactions and Quenched Spin Fluctuations in CrAs

The discovery of pressure-induced superconductivity in helimagnets (CrAs, MnP) has attracted considerable interest in understanding the relationship between complex magnetism and unconventional superconductivity. However, the nature of the magnetism and magnetic interactions that drive the unusual double-helical magnetic order in these materials remains unclear. Here, we report neutron scattering measurements of magnetic excitations in CrAs single crystals at ambient pressure. Our experiments reveal well defined spin wave excitations up to about 150 meV with a pseudogap below 7 meV, which can be effectively described by the Heisenberg model with nearest neighbor exchange interactions. Most surprisingly, the spin excitations are largely quenched above the Néel temperature, in contrast to cuprates and iron pnictides where the spectral weight is mostly preserved in the paramagnetic state. Our results suggest that the helimagnetic order is driven by strongly frustrated exchange interactions, and that CrAs is at the verge of itinerant and correlation-induced localized states, which is therefore highly pressure-tunable and favorable for superconductivity.

Chiral magnetic structure of spin-ladder multiferroic BaFe2Se3

A complex magnetic structure with specific symmetry properties is a relevant ingredient for magnetoelectric multiferroicity. In BaFe${}_{2}$Se${}_{3}$, a member of the Fe spin-ladder family of pressure-induced superconductors, the authors reveal this complexity. Using polarized and unpolarized single-crystal neutron diffraction, they evidence a chiral, umbrella-like magnetic order made of blocks of quasiferromagnetic spins, antiferromagnetically ordered along the ladder. Such accurate information on the magnetism will help to understand the magnetoelectric coupling in this family and its puzzling phase diagram.

Pressure-induced superconductivity extending across the topological phase transition in thallium-based topological materials

The coexistence of superconductivity and topology holds the potential to realize exotic quantum states of matter. Here, we report superconductivity induced by high pressure in three thallium-based materials, covering the phase transition from a normal insulator (TlBiS 2 ) to a topological insulator (TlBiSe 2 ) through a Dirac semimetal (TlBiSeS). By increasing the pressure up to 60 GPa, we observe superconductivity phase diagrams with maximal critical temperature ( T c ) values at 6.0–8.1 K. Our density functional theory calculations reveal topological surface states in superconductivity phases for all three compounds. Our study paves the path to explore topological superconductivity and topological phase transitions. • Dome-like superconductivity phase diagrams are observed in three thallium-based materials • High pressure alters electronic state and induces phase transitions in this famous family • The theoretical calculations reveal topological surface states in superconductivity phase Pei et al. report pressure-induced superconductivity in three thallium-based materials, covering the phase transition from a normal insulator to a topological insulator through a Dirac semimetal. Revealed topological surface states in superconductivity phases for all three compounds pave the path to explore topological superconductivity and topological phase transitions.

Critical topology and pressure-induced superconductivity in the van der Waals compound AuTe2Br

The study on quantum spin Hall effect and topological insulators formed the prologue to the surge of research activities in topological materials in the past decade. Compared to intricately engineered quantum wells, three-dimensional weak topological insulators provide a natural route to the quantum spin Hall effect, due to the adiabatic connection between them and a stack of quantum spin Hall insulators, and the convenience in exfoliation of samples associated with their van der Waals-type structure. Despite these advantages, both theoretical prediction and experimental identification of weak topological insulators remain scarce. Here, based on first-principles calculations, we show that AuTe2Br locates at the boundary between a strong and a weak topological semimetal state. We identify the key structural parameter that dictates the traversal of the topological transition, which can be easily realized in experiments. More interestingly, the critical topology of AuTe2Br persists up to an applied pressure of ~15.4 GPa before a structural phase transition accompanied by a change of electronic topology and the onset of superconductivity. Our results establish AuTe2Br as a new candidate for an effective tuning between weak and strong topological phases in a single material, with the potential to realize various other topological phases of matter.

Pressure-induced superconductivity in quasi-one-dimensional semimetal Ta2PdSe6

Here we report the discovery of pressure-induced superconductivity in quasi-one-dimensional ${\mathrm{Ta}}_{2}{\mathrm{PdSe}}_{6}$, through a combination of electrical transport, synchrotron x-ray diffraction, and theoretical calculations. Our transport measurements show that the superconductivity appears at a critical pressure ${P}_{\mathrm{c}}\ensuremath{\sim}18.3\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ and is robust upon further compression up to 62.6 GPa. The estimated upper critical field ${\ensuremath{\mu}}_{0}{H}_{\mathrm{c}2}(0)$ in the pressurized ${\mathrm{Ta}}_{2}{\mathrm{PdSe}}_{6}$ is much lower than the Pauli limiting field, in contrast to the case in its isostructural analogs ${M}_{2}{\mathrm{Pd}}_{\mathrm{x}}{X}_{5}$ $(M=\mathrm{Nb}, \mathrm{Ta}; X=\mathrm{S}, \mathrm{Se})$. Concomitant with the occurrence of superconductivity, anomalies in pressure-dependent transport properties are observed, including sign reversal of Hall coefficient, abnormally enhanced resistance, and dramatically suppressed magnetoresistance. Meanwhile, room-temperature synchrotron x-ray diffraction experiments reveal the stability of the pristine monoclinic structure (space group $C2$/$m$) upon compression. Combined with the density functional theory calculations, we argue that a pressure-induced Lifshitz transition could be the electronic origin of the emergent superconductivity in ${\mathrm{Ta}}_{2}{\mathrm{PdSe}}_{6}$.

Pressure-induced electronic phase transition and superconductivity in spin-ladder compounds BaFe2(S1−x Se x )3

The discovery of high-temperature superconductivity in quasi-one-dimensional spin ladder compound BaFe2S3 has attracted great attention for facilitating study on the interplay among crystalline dimensionality, magnetism, and superconductivity. Here, we report a systematic study on the doping-dependent structure, susceptibility, and high-pressure properties of BaFe2(S1−x Se x )3. The structural analysis manifests a structural transition within the doping level of 0.18 < x< 0.29. Accompanied with this structural transition, the magnetic susceptibility behaviors change substantially, in line with the antiferromagnetic structure change from the stripe-type to the block-type. Furthermore, obvious spin glassy behaviors are observed in the low-temperature region for x⩾ 0.29. High-pressure study has revealed an explicit superconductivity signal in the undoped BaFe2S3 with a pressure of about 12.6 GPa, while no bulk superconductivity is observed for the Se-doped samples. Analysis of the pressure-dependent resistance behavior indicates a pressure-induced electronic phase transition around 18 GPa for all Se-doped samples. Finally, we have discussed the possible origin for the pressure-induced superconductivity in BaFe2(S1−x Se x )3.

Quasi-uniaxial pressure induced superconductivity in the stoichiometric compound UTe2

The recent discovery of superconductivity in heavy the fermion compound ${\mathrm{UTe}}_{2}$, a candidate topological and triplet-paired superconductor, has aroused widespread interest. However, to date, there is no consensus on whether the stoichiometric sample of ${\mathrm{UTe}}_{2}$ is superconducting or not due to the lack of reliable evidence to distinguish the difference between the nominal and real compositions of samples. Here, we are the first to clarify that the stoichiometric ${\mathrm{UTe}}_{2}$ is nonsuperconducting at ambient pressure and under hydrostatic pressure up to 6 GPa; however, we find that it can be compressed into superconductivity by application of quasi-uniaxial pressure. Measurements of resistivity, magnetoresistance, and susceptibility reveal that the quasi-uniaxial pressure results in a suppression of the Kondo coherent state seen at ambient pressure, which then leads to a superconductivity initially emerged on the ab-plane at 1.5 GPa. At 4.8 GPa, the superconductivity is developed in three crystallographic directions. The superconducting state coexists with an exotic magnetic ordered state that develops just below the onset temperature of the superconducting transition. The discovery of the quasi-uniaxial pressure-induced superconductivity with an exotic magnetic state in the stoichiometric ${\mathrm{UTe}}_{2}$ not only provides new understandings of this compound, but also highlights the vital role of Te deficiency in developing the superconductivity at ambient pressures.

Distinct superconducting behaviors of pressurized WB2 and ReB2 with different local B layers

The recent discovery of superconductivity up to 32 K in the pressurized MoB2 reignites the interests in exploring high-Tc superconductors in transition-metal diborides. Inspired by that work, we turn our attention to the 5d transition-metal diborides. Here we systematically investigate the responses of both structural and physical properties of WB2 and ReB2 to external pressure, which possess different types of boron layers. Similar to MoB2, the pressure-induced superconductivity was also observed in WB2 above 60 GPa with a maximum Tc of 15 K at 100 GPa, while no superconductivity was detected in ReB2 in this pressure range. Interestingly, the structures at ambient pressure for both WB2 and ReB2 persist to high pressure without structural phase transitions. Theoretical calculations suggest that the ratio of flat boron layers in this class of transition-metal diborides may be crucial for the appearance of high Tc. The combined theoretical and experimental results highlight the effect of geometry of boron layers on superconductivity and shed light on the exploration of novel high-Tc superconductors in borides.

Pressure-Quenched Superconductivity in Weyl Semimetal NbP Induced by Electronic Phase Transitions under Pressure.

The TaAs family (NbAs, TaAs, NbP, TaP) are kinds of Weyl semimetals with lots of novel properties, thus attracting considerable attention in recent years. Here, we systematically studied the Weyl semimetal NbP up to 72 GPa through the resistivity, Raman spectra, X-ray diffraction measurements, and first-principles density functional theory (DFT) calculations. A pressure-induced semimetal-metal transition was observed at ∼36 GPa, which was further confirmed by the DFT calculations. With further compression up to 52 GPa, a superconducting state was observed. Interestingly, the Tc increases significantly upon decompression and shows a dome-shaped trend as a function of pressure. Surprisingly, the pressure-induced superconductivity can be quenched to ambient pressure, and all transitions under pressure do not involve any structural change. Our work not only depicts a phase diagram of the NbP system under high pressure but also provides a new experimental insight for superconductivity in Weyl semimetals.

Pressure-induced superconductivity and nontrivial band topology in compressed γ-InSe

We performed high-pressure electrical transport and Raman measurements on a two-dimensional rhombohedral semiconductor \ensuremath{\gamma}-InSe. Our results confirm two structural phase transitions at high pressure. More interestingly, a domelike superconducting transition with maximum ${T}_{c}$ around 2.3 K is discovered when the compound transforms to the cubic CsCl phase above 40 GPa. Our first-principles calculations indicate that the high-pressure superconducting phase possesses nontrivial topological band structure in the vicinity of the Fermi level. These results show that the physical properties in this material strongly depend on its structure, which provides insights into the interplay between superconductivity and topological physics. Our work suggests promising emergent phenomena in this material and other related III-VI semiconductors under high-pressure conditions.

Pressure-Induced Superconductivity in Flat-Band Kagome Compounds Pd3P2(S1 – x Se x )8

We performed high-pressure transport studies on the flat-band Kagome compounds, Pd3P2(S1 – x Se x )8 (x = 0, 0.25), with a diamond anvil cell. For both compounds, the resistivity exhibits an insulating behavior with pressure up to 17 GPa. With pressure above 20 GPa, a metallic behavior is observed at high temperatures in Pd3P2S8, and superconductivity emerges at low temperatures. The onset temperature of superconducting transition T C rises monotonically from 2 K to 4.8 K and does not saturate with pressure up to 43 GPa. For the Se-doped compound Pd3P2(S0.75Se0.25)8, the T C is about 1.5 K higher than that of the undoped one over the whole pressure range, and reaches 6.4 K at 43 GPa. The upper critical field with field applied along the c axis at typical pressures is about 50% of the Pauli limit, suggesting a 3D superconductivity. The Hall coefficient in the metallic phase is low and exhibits a peaked behavior at about 30 K, which suggests either a multi-band electronic structure or an electron correlation effect in the system.

High-pressure study of topological semimetals XCd2Sb2 (X = Eu and Yb)

Topological materials have aroused great interest in recent years, especially when magnetism is involved. Pressure can effectively tune the topological states and possibly induce superconductivity. Here we report the high-pressure study of topological semimetals XCd2Sb2 (X = Eu and Yb), which have the same crystal structure. In antiferromagnetic (AFM) Weyl semimetal EuCd2Sb2, the Néel temperature (T N) increases from 7.4 K at ambient pressure to 50.9 K at 14.9 GPa. When pressure is above 14.9 GPa, the AFM peak of resistance disappears, indicating a non-magnetic state. In paramagnetic Dirac semimetal candidate YbCd2Sb2, pressure-induced superconductivity appears at 1.94 GPa, then T c reaches to a maximum of 1.67 K at 5.22 GPa and drops to zero at about 30 GPa, displaying a dome-shaped temperature–pressure phase diagram. High-pressure x-ray diffraction measurement demonstrates that a crystalline-to-amorphous phase transition occurs at about 16 GPa in YbCd2Sb2, revealing the robustness of pressure-induced superconductivity against structural instability. Similar structural phase transition may also occur in EuCd2Sb2, causing the disappearance of magnetism. Our results show that XCd2Sb2 (X = Eu and Yb) is a novel platform for exploring the interplay among magnetism, topology, and superconductivity.