Singular charge fluctuations at a magnetic quantum critical point*

The heavy fermion compound YbRh₂Si₂ is well known for its large fan of linear-in-temperature “strange metal” resistivity emerging from a quantum critical point at the border of antiferromagnetic order. Previous studies revealed properties [1] that are beyond the description of the Landau framework of order parameter fluctuations, and compatible with a Kondo destruction quantum critical point [2]. Here, we probed the charge dynamics of this system by performing terahertz time-domain transmission spectroscopy experiments on high-quality YbRh₂Si₂ thin films grown by molecular beam epitaxy. We observe frequency over temperature scaling of the optical conductivity, with a critical exponent close to 1 in agreement with the linear-in-temperature dc resistivity, over a wide temperature and frequency range [3]. This dynamical scaling proves that charge carriers are a central ingredient to the singular physics at the border of antiferromagnetic order, and therefore strongly underpins the Kondo destruction nature of the observed quantum criticality.

[1] S. Paschen, T. Lühmann, S. Wirth, P. Gegenwart, O. Trovarelli, C. Geibel, F. Steglich, P. Coleman, and Q. Si, Nature 432, 881 (2004); S. Friedemann, N. Oeschler, S. Wirth, C. Krellner, C. Geibel, F. Steglich, S. Paschen, S. Kirchner, and Q. Si, Proc. Natl. Acad. Sci. USA 107, 14547 (2010).
[2] Q. Si, S. Rabello, K. Ingersent, and J. L. Smith, Nature 413, 804 (2001); P. Coleman, C. Pepin, Q. Si, and R. Ramazashvili, J. Phys. Condens. Matter 13, R723 (2001); T. Senthil, M. Vojta, and S. Sachdev, Phys. Rev. B 69, 035111 (2004).
[3] L. Prochaska, X. Li, D.C. MacFarland, A.M. Andrews, M. Bonta, E.F. Bianco, S. Yazdi, W. Schrenk, H. Detz, A. Limbeck, Q. Si, E. Ringe, G. Strasser, J. Kono, and S. Paschen, Science 367, 285 (2020).