University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Friday, November 6th 2015
12:20 pm:
Speaker: Adam Kaminski - Ames Laboratory
Subject: Interaction of electrons with collective excitations in conventional and unconventional superconductors
Please note the date and time change this week.

Interaction of electrons with collective modes plays a central role in theory of conventional superconductors and many models of unconventional superconductors. In cuprates for example, presence of such interaction was discovered almost two decades ago [1, 2], however there is no consensus as to its origin [2-5]. It is not even known whether it is responsible for driving the pairing or a mere spectator of the superconducting transition. One of the reasons for this situation is lack of momentum resolved data from classical superconductors that would serve as a baseline for identifying the physical nature of the coupling interaction and its role in the pairing mechanism. In this talk we will present such data from classical BCS superconductor MgB2 [6, 7] and review the old and new properties of the collective mode present in cuprates. In the classical superconductor, the coupling of the electrons to the phonon mode responsible for pairing remains almost unaffected across the critical temperature. This is unlike the situation in cuprates, where the signature of coupling to the collective mode vanishes above Tc. We also discovered new low energy spectral feature in MgB2 that is most likely a signature of coupling to the Leggett mode – a relative phase excitation of the two suprefluids present in this material.

[1] M. R. Norman et al., Phys. Rev. Lett. 79, 3506 (1997).
[2] M. R. Norman and H. Ding, Phys. Rev. B 57, 11089 (1998).
[3] A. Kaminski et al., Phys. Rev. Lett. 86, 1070 (2001).
[4] A. Lanzara et al., Nature 412, 510 (2001).
[5] G. H. Gweon, Nature 430, 187 (2004).
[6] D. Mou et al., Phys. Rev. B 91, 140502 (2015).
[7] D. Mou et al., Phys. Rev. B 91, 214519 (2015).

Faculty Host: Andrey Chubukov

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