Fig. 2: Effect of in-plane fields on nematicity.
From: Second order Zeeman interaction and ferroquadrupolar order in TmVO4
a Polar plot of νq as a function of field direction for constant η > 0 (green) and η < 0 (yellow). The thick blue line shows νq(ϕ) with angular-dependent η(ϕ). The diamonds indicate the two domains with negative shear strain, εxy (order parameter 〈σx〉 < 0, yellow) and positive strain (〈σx〉 > 0, green). ϕ measures the angle relative to the [110]T direction in the tetragonal unit cell, such that ϕ = 0 lies along the B2g distortion direction. Note that η ∝ εxy ∝ 〈σx〉. b Longitudinal fields induce finite order above TQ and smear out the phase transition. The ferroquadrupolar order parameter, 〈σx〉, is shown at T = 4 K > TQ as a function of field direction in the plane perpendicular to the c-axis. The order parameter vanishes only for Bx = 0 or By = 0. c Quantum critical field (blue) as a function of magnetic field direction. The two intersecting ellipses are in the Bx − Bz and By − Bz planes respectively. d Calculated phase diagram for the effective model given by Eq. (5) with ξ = 0.002T−2. Light colors correspond to 〈σx〉 = 0 and darker red corresponds to increasing values of 〈σx〉. Solid black circles correspond to the peaks indicated by the blue arrows in Fig. 3.
