The presence of optical polarization anisotropies, such as Faraday/Kerr effects, linear birefringence, and magnetoelectric birefringence are evidence for broken symmetry states of matter. The recent discovery of a Kerr effect using near-IR light in the pseudogap phase of the cuprates can be regarded as a strong evidence for a spontaneous symmetry breaking and the existence of an anomalous long-range ordered state. In this work we present a high precision study of the polarimetry properties of the cuprates in the THz regime. While no Faraday effect was found in this frequency range to the limits of our experimental uncertainty (1.3 milli-radian or 0.07• ), a small but significant polarization rotation was detected that derives from an anomalous linear dichroism. In YBa2Cu3Oy the effect has a temperature onset that mirrors the pseudogap temperature T * and is enhanced in magnitude in underdoped samples. In x = 1/8 La2−xBaxCuO4, the effect onsets above room temperature, but shows a dramatic enhancement near a temperature scale known to be associated with spin and charge ordered states. These features are consistent with a loss of both C4 rotation and mirror symmetry in the electronic structure of the CuO2 planes in the pseudogap state.PACS numbers: 74.25. Gz, 74.72.Kf, An extensive research effort has been carried out over the last two decades on defining the role and origin of the pseudogap phase in the cuprates. The pseudogap, a regime of the phase diagram generally located at higher temperatures than the superconducting state, is characterized by an energy gap in the density of states at the Fermi level as well as various transport and magnetic anomalies. Whether this gap is related to superconductivity or competes with it, and whether it realizes an additional long-range ordered state is controversial [1,2]. Characterization of a stable static order with true broken symmetry in the pseudogap regime could solve the mystery surrounding its origin.Optical polarization anisotropies, such as Faraday/Kerr effects, gyrotropic rotation, linear birefringence, and magneto-electric birefringence can be sensitive tools for the detection of broken symmetry states of matter. For instance, materials with anti-symmetric off-diagonal components in the dielectric tensor can rotate the plane of polarization of linearly polarized light. Such tensor elements are only allowed in a material that breaks either time-reversal or inversion and mirror symmetries. Such effects are referred to as circular, since the eigenmodes of their transmission or reflection matrices are left and right circular polarizations. The most common such "circular" effects are magneto-optical ones arising from time-reversal symmetry breaking from magnetic moments aligned either by applying external magnetic field or spontaneous magnetization. Another circular effect arises in so-called gyrotropic ordered materials that breaks all mirror symmetries. Spiral structures and cholesteric textures have such optical activity and can rotate polarization in the absence o...

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We investigate the field-tuned quantum phase transition in a 2D low-disorder amorphous InO(x) film in the frequency range of 0.05 to 16 GHz employing microwave spectroscopy. In the zero-temperature limit, the ac data are consistent with a scenario where this transition is from a superconductor to a metal instead of a direct transition to an insulator. The intervening metallic phase is unusual with a small but finite resistance that is much smaller than the normal state sheet resistance at the lowest measured temperatures. Moreover, it exhibits a superconducting response on short length and time scales while global superconductivity is destroyed. We present evidence that the true quantum critical point of this 2D superconductor metal transition is located at a field B(sm) far below the conventionally defined critical field B(cross) where different isotherms of magnetoresistance cross each other. The superfluid stiffness in the low-frequency limit and the superconducting fluctuation frequency from opposite sides of the transition both vanish at B≈B(sm). The lack of evidence for finite-frequency superfluid stiffness surviving B(cross) signifies that B(cross) is a crossover above which superconducting fluctuations make a vanishing contribution to dc and ac measurements.