Macroscopically inhomogeneous state at the boundary between the superconducting, antiferromagnetic, and metallic phases in quasi-one-dimensional(TMTSF)2PF6

Abstract

We report on experimental studies of the phase state and the character of phase transitions in the quasi-onedimensional organic compound (TMTSF) 2 PF 6 in the close vicinity of the borders between the metal ͑M͒, antiferromagnetic ͑AF͒ insulator, and superconducting ͑SC͒ states. In order to drive the system precisely through the phase border P 0 (T 0 ), the sample was maintained at fixed temperature T and pressure P, whereas the critical pressure P 0 was tuned by applying the magnetic field B. In this approach, the magnetic field was used ͑i͒ for smooth and precise tuning ␦PϭPϪP 0 ͓thanks to a monotonic P 0 (B) dependence͔ and ͑ii͒ for identifying the phase composition ͑due to qualitatively different magnetoresistance behavior in different phases͒. Experimentally, we measured magnetoresistance R(B) and its temperature dependence R(B,T) in the pressure range 0-1 GPa. Our studies focus on the features of the magnetoresistance at the phase transitions between the M and AF phases and in the close vicinity to the superconducting transition at TϷ1 K. We found pronounced history effects arising when the AF/M phase border is crossed by sweeping the magnetic field: the resistance depends on a trajectory which the system arrives at a given point of the P-B-T phase space. In the transition from the M to AF phase, driven by increasing magnetic field, the features of the M phase extend well into the AF phase. At the opposite transition from the AF to M phase, the features of the AF phase are observed in the M phase. These results evidence for a macroscopically inhomogeneous state, which contains macroscopic inclusions of the minority phase, spatially separated from the majority phase. When the system is driven away from the transition, the homogeneous state is restored; upon a return motion to the phase boundary, no signatures of the minority phase are observed up to the phase boundary.

Nonmagnetic high pressure cell for magnetic remanence measurements up to 1.5 GPa in a superconducting quantum interference device magnetometer

“…As transmitting-pressure medium we have chosen the widely used in high pressure experiments polyethylsiloxane liquid [16][17][18] ͑PES-1͒ providing perfectly hydrostatic conditions for the sample in the operating pressure range. As transmitting-pressure medium we have chosen the widely used in high pressure experiments polyethylsiloxane liquid [16][17][18] ͑PES-1͒ providing perfectly hydrostatic conditions for the sample in the operating pressure range.…”

Phase Separation of Superconducting Phases in the Penson–Kolb–Hubbard Model

“…All phase transition boundaries, necessary to construct the complete phase diagram for fixed µ, have been obtained numerically by comparing the grand potential (14) for the solutions found. The transition boundaries for fixed n have been determined by comparing the free energies f = Ω/N + µn for homogeneous phase (it is calculated by using (14), the concentration n is determined by (15)) and phase separated states (determined by (16)). It has been also checked that these results are consistent with the boundaries obtained from the results for fixed µ (discussed above) by determining the values of electron concentration (equation (15)) on the both sides of transition boundaries derived at fixed µ, which is thermodynamically conjugate to n.…”

“…Organic compounds also exhibit the superconductor-insulator phase separations as a result of the external pressure (e.g. quasi-one dimensional (TMTSF) 2 PF 6 [14] and (TMTSF) 2 ReO 4 [15]) and fast cooling rate through the glass-like structure transition (e. g. κ-(ET) 2 Cu[N(CN) 2 ]Br [16]).…”

Competition between triplet superconductivity and antiferromagnetism in quasi-one-dimensional electron systems

“…55 we compare this to the experimental phase diagram of ͑TMTSF͒ 2 PF 6 . 10,11 One consequence of having enhanced symmetry at a phase transition is the suppression of the critical temperature due to fluctuations of one order parameter into the other. This may contribute to the drastic drop in T AF as pressure is increased near the AF/ TSC phase boundary in Bechgaard salts.…”

“…The most well studied material from this family ͑TMTSF͒ 2 PF 6 is an antiferromagnetic insulator at ambient pressure and becomes a superconductor at high pressure. [7][8][9][10][11] The symmetry of the superconducting order parameter in ͑TMTSF͒ 2 PF 6 is not yet fully established, 12 but there is strong evidence that electron pairing is spin triplet: the superconducting T c is strongly suppressed by disorder; [13][14][15][16][17] critical magnetic field H c2 in the interchain direction exceeds the paramagnetic limit; 18,19 the electron spin susceptibility, obtained from the Knight shift measurements, does not decrease below T c . 20 In another material from this family, ͑TMTSF͒ 2 ClO 4 , superconductivity is stable at ambient pressure and also shows signatures of triplet pairing.…”