Superconductor-Insulator Transition in a Parallel Magnetic Field

Wu, Wenhao; Adams, P. W.

doi:10.1103/physrevlett.73.1412

Cited by 62 publications

(70 citation statements)

References 23 publications

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“…Note that the upsweep branch (superheating branch) of the hysteresis loop is interspersed with many avalanche-like jumps in resistance, whereas the down sweep branch (supercooling branch) is somewhat smoother. These jumps are similar to what has been observed in previous transport studies of Al films having substantially more disorder than the ones used in this study [5,6]. Since the film thicknesses is much less than the coherence length, the jumps are not due superconducting vortex motion nor to magnetic flux dynamics.…”

Section: Sample Preparationsupporting

confidence: 89%

“…In this limit, the critical field transition is Zeeman mediated. Studies of Zeeman-limited superconductivity in low atomic mass elemental metal films have revealed several interesting effects, including a hysteretic first-order critical field transition [5,6], incoherent Cooper pairing [7,8], reentrance [9], and excess sub-gap states [10]. Here, we present resistivity and tunneling density of states measurements across the hysteretic Zeeman critical field transition in ultra-thin Al films.…”

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confidence: 99%

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Asymmetric Avalanche Behavior in a Zeeman-Limited Superconductor

Adams¹,

Prestigiacomo²

2014

J. Phys.: Conf. Ser.

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Abstract. We have performed transport and tunneling density of states measurements of ultra-thin Al films through the first-order parallel critical field transition. The transition is intrinsically hysteretic and exhibits avalanche-like jumps in both resistivity and tunneling density states. Tunneling measurements on films with sheet resistances of a few hundred ohms show large avalanche-like collapses of the condensate on the superheating branch of the critical field hysteresis loop. In contrast, the transition back into the superconducting phase (i.e., along the supercooling branch) is always continuous. IntroductionThe response of a superconductor to a magnetic field that only couples to the electron's spin, sometimes referred to as a Zeeman field, remains a subject of significant interest [1,2]. In practice, if one applies a magnetic field to a superconducing film whose thickness is much less than the coherence length, then the primary coupling between the field and the condensate is through the Zeeman splitting of the conduction electrons. The film geometry suppresses the Miessner response and the parallel field cannot induce screening currents, nor can quantized vortices enter the system. In this limit, the critical field transition is Zeeman mediated. Studies of Zeeman-limited superconductivity in low atomic mass elemental metal films have revealed several interesting effects, including a hysteretic first-order critical field transition [5,6], incoherent Cooper pairing [7,8], reentrance [9], and excess sub-gap states [10]. Here, we present resistivity and tunneling density of states measurements across the hysteretic Zeeman critical field transition in ultra-thin Al films. As the normal state is approached, we observe large avalanches in the density of states indicating that macroscopic regions of superconductivity suddenly and irreversibly collapse. In contrast, the transition from the normal state to the superconducting state is smooth and continuous.In this study a magnetic field was applied parallel to the surface of superconducting Al films having a thickness that was approximately 5 times smaller than the coherence length (ξ ∼ 20 nm). In this limit, the orbital response to the field is suppressed, and the transition occurs when the Zeeman splitting is of the order of the superconducting gap ∆ 0 [11]. The conventional picture is that this Zeeman mediated transition, which is often referred to as the spin-paramagnetic (S-P) transition, occurs between a BCS ground state with a homogenous order parameter and a polarized Fermi liquid normal state. At low temperatures the Zeeman critical field is expected to be near the Clogston-Chandrasekhar value H c = ∆ 0 / √ 2µ B [12]. As we show below, the

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Section: Sample Preparationsupporting

confidence: 89%

mentioning

confidence: 99%

Asymmetric Avalanche Behavior in a Zeeman-Limited Superconductor

Adams¹,

Prestigiacomo²

2014

J. Phys.: Conf. Ser.

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“…In the case of ultrathin films (with thicknesses of a few nm) the magnetic behavior can be quite different because the orbital currents are suppressed, and the transition to the normal state is driven by coupling of the magnetic field to the electronic spins. Under such circumstances, the critical field transition can be strongly hysteretic, below a tricritical point [26]. However, close to T c , there is no hysteresis, and if the films are very pure it is still possible to observe very sharp transitions, with well defined critical fields (defined to within a few parts in a thousand) [27].…”

Section: Appendix A: Magnetic Properties Of Type I Superconductorsmentioning

confidence: 99%

Variations of Casimir energy from a superconducting transition

et al. 2005

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We consider a five-layer Casimir cavity, including a thin superconducting film. We show that when the cavity is cooled below the critical temperature for the onset of superconductivity, the sharp variation (in the microwave region) of the reflection coefficient of the film produces a variation in the value of the Casimir energy. Even though the relative variation in the Casimir energy is very small, its magnitude can be comparable to the condensation energy of the superconducting film, and thus causes a significant increase in the value of the critical magnetic field, required to destroy the superconductivity of the film. The proposed scheme might also help clarifying the current controversy about the magnitude of the contribution to Casimir free energy from the TE zero mode, as we find that alternative treatments of this mode strongly affect the shift of critical field.

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“…Though the films are too disordered to support a FFLO phase [8], they are a model system for studying the spin states of BCS superconductivity in the presence of a non-negligible Zeeman field that ultimately drives the first-order spin-paramagnetic transition associated with H c|| [8,9] and the long conjectured FFLO regime just above H c|| [8]. Tunneling measurements in fields H || 1 2 H c|| reveal a subgap peak in the DOS spectrum, shifted down from the primary BCS peak by the Zeeman energy.…”

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confidence: 99%

Field-Induced Spin Mixing in Ultrathin Superconducting Al and Be Films in High Parallel Magnetic Fields

2004

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We report spin-dependent electron density of states (DOS) studies of ultra-thin superconducting Al and Be films in high parallel magnetic fields. Superconductor-insulator-superconductor (SIS) tunneling spectra are presented in which both the film and the counterelectrode are in the paramagnetic limit. This SIS configuration is exquisitely sensitive to spin mixing and/or spin flip processes which are manifest as DOS singularities at eV = 2∆o ± eVz. Both our Al and Be data show a well defined subgap peak whose magnitude grows dramatically as the parallel critical field is approached. Though this feature has previously been attributed to spin-orbit scattering, it is more consistent with fluctuations into a field induced mixed-spin state. [3,4], research on systems exhibiting a nontrivial interplay between magnetism and superconductivity has moved to the forefront on condensed matter physics. In this Letter we probe the spin states of superconducting Al and Be films in high parallel magnetic fields via spin polarized electron tunneling measurements [5]. The films are sufficiently thin so as to restrict the transverse motion of electrons, thus allowing us to access the high field regime while maintaining time reversal symmetry [6] up to the Clogston-Chandrasekhar critical field, where g is the Landé g-factor, µ B is the Bohr magneton, and ∆ o is the superconducting gap [7]. Though the films are too disordered to support a FFLO phase [8], they are a model system for studying the spin states of BCS superconductivity in the presence of a non-negligible Zeeman field that ultimately drives the first-order spin-paramagnetic transition associated with H c|| [8,9] and the long conjectured FFLO regime just above H c|| [8]. Tunneling measurements in fields H || 1 2 H c|| reveal a subgap peak in the DOS spectrum, shifted down from the primary BCS peak by the Zeeman energy. The magnitude of the satellite peak varies as the square root of the reduced field. Though this peak has previously been attributed to spin-orbit (SO) scattering in Al [10], it is also manifest in the much lighter element Be, suggesting that it is a property of the high field condensate.In the mid 1970's Tedrow, Meservey, and coworkers conducted a series of tunneling experiments on paramagnetically limited Al films. They showed that the tunneling spectrum of a superconductor-insulator-superconductor (S-I-S) junction, in which both the film and the counter-electrode are thin, will not exhibit a Zeeman splitting so long as there is no spin mixing or spin flip processes [8]. Assuming that the gap is ∆ o on either side of the junction, then the tunneling spectrum has a single BCS peak at the usual |eV | = 2∆ o , independent of the Zeeman energy eV z = gµ B H || , where e is the electron charge. If, however, there is spin flip during the tunneling, then satellite peaks will appear at energies |eV | = 2∆ o ± eV z [8,10]. Similarly, if there is a mechanism by which the spin eigenstates are partially mixed, then there will be a minority-spin satellite peak in the sp...

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Superconductor-Insulator Transition in a Parallel Magnetic Field

Cited by 62 publications

References 23 publications

Asymmetric Avalanche Behavior in a Zeeman-Limited Superconductor

Asymmetric Avalanche Behavior in a Zeeman-Limited Superconductor

Variations of Casimir energy from a superconducting transition

Field-Induced Spin Mixing in Ultrathin Superconducting Al and Be Films in High Parallel Magnetic Fields

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