Signature of quantum criticality in cuprates by charge density fluctuations.

The universality of the strange metal phase in many quantum materials is often attributed to the presence of a quantum critical point (QCP), a zero-temperature phase transition ruled by quantum fluctuations. In cuprates, where superconductivity hinders direct QCP observation, indirect evidence comes from the identification of fluctuations compatible with the strange metal phase. Here we show that the recently discovered charge density fluctuations (CDF) possess the right properties to be associated to a quantum phase transition.

Discovery of charge order in a cuprate Mott insulator.

Copper oxide superconductors universally exhibit multiple forms of electronically ordered phases that break the native translational symmetry of the CuO planes. In underdoped cuprates with correlated metallic ground states, charge/spin stripes and incommensurate charge density waves (CDWs) have been experimentally observed over the years, while early theoretical studies also predicted the emergence of a Coulomb-frustrated 'charge crystal' phase in the very lightly doped, insulating limit of CuO planes. Here, we search for signatures of CDW order in very lightly hole-doped cuprates from the 123 family BaCuO (BCO; : Y or rare earth), by using resonant X-ray scattering, electron transport, and muon spin rotation measurements to resolve the electronic and magnetic ground states fully.

Mn-Rich MnSb Te : A Topological Insulator with Magnetic Gap Closing at High Curie Temperatures of 45-50 K.

Ferromagnetic topological insulators exhibit the quantum anomalous Hall effect, which is potentially useful for high-precision metrology, edge channel spintronics, and topological qubits.  The stable 2+ state of Mn enables intrinsic magnetic topological insulators. MnBi Te is, however, antiferromagnetic with 25 K Néel temperature and is strongly n-doped.

Dynamic electron correlations with charge order wavelength along all directions in the copper oxide plane.

In strongly correlated systems the strength of Coulomb interactions between electrons, relative to their kinetic energy, plays a central role in determining their emergent quantum mechanical phases. We perform resonant x-ray scattering on BiSrCaCuO, a prototypical cuprate superconductor, to probe electronic correlations within the CuO plane. We discover a dynamic quasi-circular pattern in the x-y scattering plane with a radius that matches the wave vector magnitude of the well-known static charge order.

Transition from a uni- to a bimodal interfacial charge distribution in [Formula: see text]/[Formula: see text] upon cooling.

We present a combined resonant soft X-ray reflectivity and electric transport study of [Formula: see text]/[Formula: see text] field effect devices. The depth profiles with atomic layer resolution that are obtained from the resonant reflectivity reveal a pronounced temperature dependence of the two-dimensional electron liquid at the [Formula: see text]/[Formula: see text] interface. At room temperature the corresponding electrons are located close to the interface, extending down to 4 unit cells into the [Formula: see text] substrate.