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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:0
UID:UW-Physics-Event-5168
DTSTART:20190912T160000Z
DURATION:PT1H0M0S
DTSTAMP:20260415T070735Z
LAST-MODIFIED:20190905T011108Z
LOCATION:5310 Chamberlin Hall
SUMMARY:Transport properties of a compensated metal: the Lorentz ratio
  and the absence of mass renormalization near a Pomeranchuk quantum cr
 itical point\, R. G. Herb Condensed Matter Seminar\, Songci Li \, UW-M
 adison
DESCRIPTION:A violation of the Wiedemann-Franz law in a metal can be q
 uantified by comparing the Lorentz ratio\, $L=kapparho/T$. We obtain t
 he Lorentz ratio of a clean compensated metal with intercarrier intera
 ction as the dominant scattering mechanism by solving exactly the syst
 em of coupled integral Boltzmann equations. The Lorentz ratio is shown
  to assume a particular simple form in the forward-scattering limit: $
 L/L_0=overline{Theta^2}/2$\, where $Theta$ is the scattering angle. In
  this limit\, $L/L_0$ can be arbitrarily small. We discuss how a stron
 g downward violation of the Wiedemann-Franz law in a type-II Weyl semi
 metal WP$_2$ can be explained within our model. In the second part of 
 the talk\, we discuss the role of mass renormalization in electron tra
 nsport of a compensated metal near a QCP. According to a naive interpr
 etation of the Drude formula\, as electrons get heavier near a QCP\, t
 heir electrical and thermal conductivities decrease. However\, this pi
 cture has never been supported by an actual calculation. We employ a m
 odel case of a compensated metal near a Pomeranchuk-type QCP. The adva
 ntage of this model is that it allows one to treat electrical and ther
 mal conductivities on the same footing\, without invoking umklapp scat
 tering or any other channels of momentum relaxation which are extraneo
 us to the electron system. By solving the kinetic equations\, we obtai
 n explicit results for the electrical and thermal conductivities of a 
 two-band compensated metal. We show that mass renormalization factors 
 cancel out with the $Z$ factors\, which renormalize the scattering pro
 bability\, so that all the transport quantities contain the bare rathe
 r than renormalized electron masses. We also demonstrate how the same 
 conclusion can be drawn by diagrammatically calculating the optical co
 nductivity.
URL:https://www.physics.wisc.edu/events/?id=5168
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