UBe13 and U1−xThxBe13: Unconventional Superconductors

Stewart, G. R.

doi:10.1007/s10909-018-02140-z

Cited by 18 publications

(9 citation statements)

References 72 publications

(221 reference statements)

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“…This however means that the two transitions should cross rather than split, as suggested by the dotted line in figure 4 even though within the experimental sensitivity no indication of TS2 lying below TS1 is seen at low pressure. In this, UTe2 resembles more the case of UBe13, where a small amount of doping with thorium apparently splits the single superconducting transition into two separate transitions [21,22], but in fact an observed change in the order parameter implies the existence of a fourth line in the phase diagram even though no transition has been directly detected [21,23,24]. We have sketched a similar line with a question mark in figure 4.…”

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confidence: 80%

Multiple superconducting phases in a nearly ferromagnetic system

et al. 2019

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Multiple superconducting order parameters are extremely rare. Here we show that a very small pressure can induce this phenomenon in the recently discovered heavy fermion superconductor UTe2. This nearly ferromagnetic system shows several intriguing phenomena, including an extraordinary reinforcement of superconductivity in very strong magnetic fields. We find that pressure can tune the system to a more correlated state and probable magnetic order. The superconducting critical temperature is strongly enhanced, reaching almost 3K, a new record for Ce-and U-based heavy fermion superconductors. Most spectacularly under pressure we find a transition within the superconducting state, putting UTe2 among the very rare systems having multiple superconducting phases. UTe2 under pressure is a treasure trove of several of the most fascinating phenomena in unconventional superconductivity and may well be a keystone in their understanding.In most superconductors the superconducting order parameter is s-wave, meaning it has the same symmetry as the crystal lattice. However in the ever expanding family of unconventional superconductors, which includes such disparate members as high-Tc cuprates and pnictides, organic superconductors, and heavy fermions, the order parameter can assume a number of different symmetries, usually lower than the lattice symmetry. This opens the intriguing possibility that a given system could in principle exhibit different order parameters, each one being selected by changing an external variable like temperature or magnetic field. This scenario does in fact exist, but is extremely rare, having been really established only in superfluid 3 He[1] and in two superconductors: UPt3[2,3] and thorium-doped UBe13 [4]. The recently discovered superconductivity in the heavy fermion system UTe2 [5] shows several unusual properties, the most spectacular being re-entrant superconductivity when magnetic fields as high as 60 Tesla are applied in specific directions [6][7][8][9]. Another intriguing property is the temperature dependence of the specific heat. Indeed in all samples a large residual term, of about 50% of the normal state specific heat, seems to remain as the temperature approaches zero [5,6].In this report we show that the superconductivity is extremely sensitive to hydrostatic pressure as a tuning parameter and that UTe2 is probably another example of multiple superconducting phases. The superconducting state found at zero pressure is monotonously depressed with pressure but a second superconducting state is found to emerge as pressure is increased. Pressure increases the splitting between the 2 transitions and the high temperature superconducting transition reaches nearly 3K, a new record for a U-based heavy fermion superconductor. Pressure also drives the system towards a more correlated state, with evidence for a strong enhancement of the electronic effective mass. At a critical pressure of about 1.7 GPa both superconducting states are suppressed and a new order parameter, probably magnetic, is foun...

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confidence: 80%

Multiple superconducting phases in a nearly ferromagnetic system

et al. 2019

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“…In fact, this technique has been used to observe a collective mode of unknown origin in the heavy-fermion superconductor UBe 13 [59]. To date, there is no evidence that the superconducting state of this system is TRSB, but a split transition has been reported in specific heat measurements of its Th-doped relative U 1−x Th x Be 13 [60], which are suggestive of a multicomponent order as discussed in section I. In light of this, it could be interesting to revisit the order parameter symmetry of these compounds and whether time-reversal symmetry is broken.…”

Section: A Relative Phase Modementioning

confidence: 99%

Spectroscopic signatures of time-reversal symmetry breaking superconductivity

Poniatowski,

Curtis,

Yacoby

et al. 2021

Preprint

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The collective mode spectrum of a symmetry-breaking state, such as a superconductor, provides crucial insight into the nature of the order parameter. In this context, we present a microscopic weak-coupling theory for the collective modes of a generic multi-component time-reversal symmetry breaking superconductor, and show that fluctuations in the relative amplitude and phase of the two order parameter components are well-defined underdamped collective modes, even in the presence of nodal quasiparticles. We then demonstrate that these "generalized clapping modes" can be detected using a number of experimental techniques including ac electronic compressibility measurements, ultrafast THz spectroscopy, and microwave power absorption. Finally, we discuss the implications of our work as a new form of "collective mode spectroscopy" that drastically expands the number of experimental probes capable of detecting time-reversal symmetry breaking in unconventional superconductors such as Sr2RuO4, UTe2, and moiré heterostructures.

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“…Multiband pairing which breaks time-reversal symmetry has been suggested for various centrosymmetric materials of high current interest, for example iron-based superconductors [5][6][7][8][9][10][11] and Sr 2 RuO 4 [12][13][14]. A particularly interesting candidate is U 1−x Th x Be 13 [15], which shows two transitions in a certain doping range [16,17], where time-reversal symmetry is broken in the low-temperature phase [18]. Moreover, the observation that the specific heat and the thermal conductivity are linear in temperature under pressure [19] hint at the existence of BFSs [20].…”

Section: Introductionmentioning

confidence: 99%

Distortional weak-coupling instability of Bogoliubov Fermi surfaces

2021

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Centrosymmetric multiband superconductors which break time-reversal symmetry generically have two-dimensional nodes, i.e., Fermi surfaces of Bogoliubov quasiparticles. We show that the coupling of the electrons to the lattice always leads to a weak-coupling instability of such a state towards spontaneous breaking of inversion symmetry at low temperatures. This instability is driven by a Cooper logarithm in the internal energy but the order parameter is not superconducting but distortional. We present a comprehensive symmetry analysis and introduce a measure that allows to compare the strengths of competing distortional instabilities. Moreover, we discuss the instability using an effective single-band model. This framework reveals a duality mapping of the effective model which maps the distortional order parameter onto a superconducting one, providing a natural explanation for the Cooper logarithm and the weak-coupling nature of the instability. Finally, we consider the possibility of a pair-density wave state when inversion symmetry is broken. We find that it can indeed exist but does not affect the instability itself.

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UBe13 and U1−xThxBe13: Unconventional Superconductors

Cited by 18 publications

References 72 publications

Multiple superconducting phases in a nearly ferromagnetic system

Multiple superconducting phases in a nearly ferromagnetic system

Spectroscopic signatures of time-reversal symmetry breaking superconductivity

Distortional weak-coupling instability of Bogoliubov Fermi surfaces

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