Pressure-Induced Unconventional Superconducting Phase in the Topological InsulatorBi2Se3

Abstract

Simultaneous low-temperature electrical resistivity and Hall effect measurements were performed on single-crystalline Bi2Se3 under applied pressures up to 50 GPa. As a function of pressure, superconductivity is observed to onset above 11 GPa with a transition temperature Tc and upper critical field Hc2 that both increase with pressure up to 30 GPa, where they reach maximum values of 7 K and 4 T, respectively. Upon further pressure increase, Tc remains anomalously constant up to the highest achieved pressure. Conversely, the carrier concentration increases continuously with pressure, including a tenfold increase over the pressure range where Tc remains constant. Together with a quasilinear temperature dependence of Hc2 that exceeds the orbital and Pauli limits, the anomalously stagnant pressure dependence of Tc points to an unconventional pressureinduced pairing state in Bi2Se3 that is unique among the superconducting topological insulators. PACS numbers:The interplay between superconductivity and topological insulator (TI) surface states has recently received enormous attention due to the observation of the long sought Majorana quasiparticle in InSb nanowires [1] and the promise of realizing topologically protected quantum computation [2]. Characterized by a nontrivial Z2 band topology with a bulk insulating energy gap that leads to a chiral metallic surface state with spin-momentum locking, TI surface states are analogous to the quantum Hall edge state and arise at the surface of a TI material due to the topological nature of the crossover between a nontrivial bulk insulating gap and the trivial insulating gap of the vacuum [3]. The use of the proximity effect [4][5][6][7] to induce superconductivity in Bi 2 Se 3 , the most well studied TI material to date, has had success in coupling these two states but suffers from the presence of bulk conducting states which require gating to realize true TI supercurrents [8].Theoretically, nontrivial surface Andreev bound states can be directly realized by opening a superconducting energy gap in a bulk conductor [9], which is why the quest for the topological superconductor is one of the most active areas in condensed-matter physics. Recently, superconductivity has been found in materials with topologically nontrivial band structures, such as in Cu x Bi 2 Se 3 [10-13] and YPtBi [14,15], providing not only intrinsic systems with which to study the interplay between superconductivity and TI states, but also the potential to realize a new class of odd-parity, unconventional superconductivity [9].The application of pressure has also uncovered superconductivity in several related materials, such as elemen- route to realizing topological superconductivity. In this study, we measure transport properties of Bi 2 Se 3 over an extended pressure range to investigate the ground state at ultrahigh pressures by using a designer diamond anvil cell capable of measuring both longitudinal and transverse resistivities up to 50 GPa. We observe the onset of a superconducting phase above 11 GPa...

Pressure-induced superconductivity in the three-dimensional topological Dirac semimetal Cd3As2

“…7,8 Under pressure, Bi 2 Te 3 , Bi 2 Se 3 , Sb 2 Te 3 and Sb 2 Se 3 become superconducting, which are also regarded as candidates for TSCs. [9][10][11][12][13][14] Note that there are debates on whether these candidates are indeed TSCs, [9][10][11][12][13][14][15][16][17] therefore further experimental works are needed to definitely identify a TSC and manipulate the Majorana fermions on its surface.…”

Evolution of the topologically protected surface states in superconductorβ-Bi2Pd from the three-dimensional to the two-dimensional limit

“…The proposed candidate TSCs have been realized by introducing carriers into topological insulators, such as Cuintercalated Bi 2 Se 3 [34][35][36][37] and In-doped SnTe [38], or by applying pressure to topological parent compounds, such as Bi 2 Te 3 , Sb 2 Te 3 , and Bi 2 Se 3 [39][40][41][42]. More recently, two members of the Bi-Pd family of superconductors have been found to exhibit topologically protected surface states with Rashba-like spin splitting.…”

Effect of pressure on superconductivity in the indium-doped topological crystalline insulator SnTe

“…Superconductivity appears in Bi 2 Se 3 at ∼13.5 GPa at a transition temperature of 0.5 K, which gradually increases to a maximum of 7 K on increasing pressure up to 30 GPa. At higher pressures, the T c remains almost constant up to 50 Gpa [10]. Bi 2 Te 3 is another topological insulator, for which superconductivity is reported around 3 K under 3 GPa pressure that increases to 8 K at 15 GPa and for further higher pressures the T c exhibits a decreasing trend [12].…”

“…This has led to the discovery of superconductivity in myriad compounds at high pressure [10][11][12]. With regard to optimally doped superconductors, such studies could reflect if there is a 'dome structure' associated with phase transitions visá vis carrier concentration that relates to quantum criticality and correlation effects [13].…”

“…In particular, topological surface states have been investigated in Bi 2 Se 3 and Bi 2 Te 3 which have been driven to a superconducting state with application of external pressure [10][11][12]. In undoped topological insulators, superconductivity is achieved at relatively high pressure.…”