Ambient Pressure Structural Quantum Critical Point in the Phase Diagram of(CaxSr1−x)

Abstract

The quasi-skutterudite superconductor Sr3Rh4Sn13 features a pronounced anomaly in electrical resistivity at T * ∼138 K. We show that the anomaly is caused by a second-order structural transition, which can be tuned to 0 K by applying physical pressure and chemical pressure via the substitution of Ca for Sr. A broad superconducting dome is centred around the structural quantum critical point. Detailed analysis of the tuning parameter dependence of T * as well as insights from lattice dynamics calculations strongly support the existence of a structural quantum critical point at ambient pressure when the fraction of Ca is 0.9 (i.e., xc = 0.9). This establishes (CaxSr1−x)3Rh4Sn13 series as an important system for exploring the physics of structural quantum criticality without the need of applying high pressures.Quantum criticality associated with a second-order phase transition at zero temperature has been a fruitful concept in the search for superconductivity. Particularly clear examples include the heavy fermion [1, 2] and iron-based systems [3][4][5][6], where superconductivity is stabilized in the vicinity of an antiferromagnetic quantum critical point (QCP). In addition to magnetic instabilities, structural instabilities also have an intricate influence on superconductivity. However, clean systems with continuous structural transition tunable by external parameters are relatively rare, and for the few cases studied in recent years, the structural order is found in the vicinity of magnetic order [7], making the notion of structural quantum criticality and its influence on the superconductivity less advanced than the magnetic counterpart.Superconducting stannides [8,9], including A 3 T 4 Sn 13 systems where A=La,Sr,Ca and T=Ir,Rh, have recently been reexamined using a wide range of probes [10][11][12][13][14][15][16][17][18][19][20][21][22]. Sr 3 Rh 4 Sn 13 , a member of this stoichiometry family, is a strong-coupling superconductor with a critical temperature T c ≈4.7 K. The superconducting gap function ∆ is nodeless, with 2∆/k B

Strong enhancement ofs-wave superconductivity near a quantum critical point ofCa3Ir4Sn13

“…Recently, it has been reported that the series (Ca 1−x ,Sr x ) 3 Rh 4 Sn 13 has a very similar phase diagram with a quantum critical point which should appear at ambient pressure if the Ca fraction is 0.9 [15]. This opens the possibility to study the interplay of superconductivity, CDW and quantum criticality over a broader interval of pressures up and beyond the region where superconductivity is strongest and the critical temperature reaches its maximum.…”

“…The vicinity to unconventional superconductors is possibly related to the competing CDW state or to the presence of a quantum phase transition. Remarkably the investigated system is placed in the Uemura plot close to 7 V 3 Si, another phonon-mediated superconductor with a nearby structural instability.Recently, it has been reported that the series (Ca 1−x ,Sr x ) 3 Rh 4 Sn 13 has a very similar phase diagram with a quantum critical point which should appear at ambient pressure if the Ca fraction is 0.9 [15]. This opens the possibility to study the interplay of superconductivity, CDW and quantum criticality over a broader interval of pressures up and beyond the region where superconductivity is strongest and the critical temperature reaches its maximum.…”

“…The quasiskutteridite cubic superconductor (Ca,Sr) 3 Ir 4 Sn 13 and the related (Ca,Sr) 3 Rh 4 Sn 13 have recently attracted attention because of the presence of a pressure induced structural phase transition at a temperature T * , the possible coexistence of superconducting and charge density wave states, and a putative quantum critical point [8][9][10][11][12][13][14][15][16]. The role and interplay of these degrees of freedom remain a central issue also in many unconventional superconductors, as demonstrated by the recent observation of CDW in HgBa 2 CuO 4+δ [17] and of competition between superconductivity and charge order in YBa 2 Cu 3 O 6.67 [18].…”

Effect of atomic disorder and Ce doping on superconductivity ofCa3Rh4Sn13: Electric transport properties under high pressure

“…Refs. 14,15 ) as a structural transition from simple cubic to I43d bcc structure, involving crystallographic cell doubling. Fig.…”

Second-order structural transition in the superconductorLa3Co4Sn13

“…Superconducting stannides [1,2] with stoichiometry A 3 T 4 Sn 13 (A = La, Sr, Ca and T = Co, Rh, Ir) have received a renewed attention owing to the discovery of a structural transition that can be tuned to 0 K [3][4][5]. In Sr 3 Ir 4 Sn 13 and Sr 3 Rh 4 Sn 13 , the structural transition occurs at T * 147 [3,6] and 138 K [4,7], respectively.…”