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Highlights • In the cuprates an unusual superconducting state is discovered. • The critical temperature is determined by the superfluid density. • These finding defy the standard Bardeen–Cooper–Schrieffer theory. • The metallic state above T c is also anomalous ('nematic'). Abstract Over the course of three decades of intense study, apart from the exceptionally high critical temperature, many unusual properties of cuprates have been discovered, notably including resistivity linear in temperature, electronic Raman continuum and optical absorption extending throughout the infrared region, pseudogap, hour-glass spin excitation spectrum, etc. However, each of these features have been also observed in other materials, including some that are not even superconducting at all. Here, we describe an extensive experiment in which over 2000 films of the La 2 − x Sr x CuO 4 have been synthesized and studied in detail over the course of the last twelve years. We argue that, uniquely, in the cuprates an unusual superconducting state, that defies the standard BCS description, develops from an unusual metallic state, in which the rotational symmetry of the electron fluid is spontaneously broken. [ABSTRACT FROM AUTHOR]

We have synthesized LaSrCuO thin films using atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The films are high-quality-singe crystal, atomically smooth, and very homogeneous. The critical temperature ( T ) shows a very little (<1 K) variation within a film of 10×10 mm area. The large statistics (over 2000 films) is crucial to discern intrinsic properties. In these films, we have measured the absolute value of the magnetic penetration depth λ with the accuracy better than 1 % and mapped densely the entire overdoped side of the LaSrCuO phase diagram. A new scaling law is established accurately for the dependence of T on the superfluid density. The scaling we observe is incompatible with the standard Bardeen-Cooper-Schrieffer picture and points to local pairing. [ABSTRACT FROM AUTHOR]

Since the discovery of high-temperature superconductivity in cuprates, proposals have been made that pairing may be local, in particular in underdoped samples. Here, we briefly review evidence for local pairs from our experiments on thin films of La Sr CuO , synthesized by atomic layer-by-layer molecular beam epitaxy (ALL-MBE). [ABSTRACT FROM AUTHOR]

We describe an extensive experimental study of La 2- x Sr x CuO 4 films synthesized by molecular beam epitaxy and investigated by angle-resolved measurements of transverse resistivity (without applied magnetic field). The data show that an unusual metallic state, in which the rotational symmetry of the electron fluid is spontaneously broken, occurs in a large temperature and doping region. The superconducting state always emerges out of this nematic metal state. [ABSTRACT FROM AUTHOR]