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Observations of spontaneous breaking of the rotational symmetry in an electron fluid, the so-called "electronic nematicity," have been reported in several quantum materials. We have developed several different methods, based on angle-resolved transport measurements, to determine the amplitude and the director of the nematic order. We present methods that are applicable to thin films or single crystals, illustrate them with transport data obtained on copper oxide superconductors, and discuss their relative advantages and disadvantages. [ABSTRACT FROM AUTHOR]

The observation of nonzero voltage transverse to the current flow, in zero magnetic field, is a sensitive indication of the nematic order in cuprate superconductors. But this effect should be carefully identified and differentiated from various conceivable experimental artifacts. Here we discuss in detail the five types of artifacts commonly encountered in transport experiments and explain how we rule out these possibilities by decisive experimental evidence. [ABSTRACT FROM AUTHOR]

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]

For overdoped cuprates, it is believed that the normal state behaves as an ordinary Fermi liquid while the superconducting state conforms to the BCS theory. We have put these beliefs to the test by a comprehensive experiment in which over two thousand cuprate films were synthesized by molecular beam epitaxy and studied in great detail and precision. Here, we compare our key experimental results to various proposed explanations based on BCS theory extended to dirty d-wave superconductors, including the cases of strong (unitary) and weak (Born) scattering on impurities. The discrepancies seem insurmountable, and point to the need to develop the theory further, likely beyond the canonical BCS paradigm. [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 used atomic-layer molecular beam epitaxy to synthesize bilayers of a cuprate metal (La1.55Sr0.45CuO4) and a cuprate insulator (La2CuO4), in which each layer is just one unit cells thick. We have studied the magnetic field and temperature dependence of the complex sheet conductance, of these films. Experiments have been carried out at frequencies between 2 and 50 MHz using the single-spiral coil technique. We found that: (i) the inductive response starts at T = 3K lower temperatures than Re s(T), which in turn is characterized by a peak close to the transition, (ii) this shift is almost constant with magnetic field up to 14 mT; (iii) T increases sharply up to 4K at larger fields and becomes constant up to 8 T; (iv) the vortexdiffusion constant D(T) is not linear with T at low temperatures as in the case of free vortices, but is rather exponential due to pinning of vortex cores, and (v) the dynamic Berezinski-Kosterlitz-Thouless (BKT) transition temperature occurs at the point where Y = (1ω/ξ+)². Our experimental results can be described well by the extended dynamic theory of the BKT transition and dynamics of bound vortex-antivortex pairs with short separation lengths. [ABSTRACT FROM AUTHOR]

We used atomic-layer molecular beam epitaxy to synthesize bilayers of a cuprate metal (La1.55Sr0.45CuO4) and a cuprate insulator (La2CuO4) film, in which each layer is just one unit cell thick. We have studied the magnetic field and temperature dependences of the complex sheet conductance, σ(ω), of these films. Experiments have been carried out at frequencies between 2 and 20 MHz using the single-spiral coil technique. We found that (i) the inductive response,Lk-1(T), starts at 1.7 K lower temperatures than Reσ(T), which in turn is characterized by a peak close to the transition, (ii) this shift is almost constant with magnetic field up to 8 T; (iii) the vortex diffusion constant D(T) is not linear with T at low temperature, as in the case of free vortices, but rather is exponential due to pinning of vortex cores, and (iv) the Berezinski-Kosterlitz-Thouless (BKT) transition temperature occurs at the point where Y = (Ιω/ξ+)2 = 1. Our experimental results can be described well by the extended dynamic theory of the BKT transition and the dynamics of bound vortex-antivortex pairs with short separation lengths. [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]

Helium ion beams (HIB) focused to subnanometer scales have emerged as powerful tools for high-resolution imaging as well as nanoscale lithography, ion milling, or deposition. Quantifying irradiation effects is an essential step toward reliable device fabrication, but most of the depth profiling information is provided by computer simulations rather than the experiment. Here, we demonstrate the use of atomic force microscopy (AFM) combined with scanning near-field optical microscopy (SNOM) to provide three-dimensional (3D) dielectric characterization of high-temperature superconductor devices fabricated by HIB. By imaging the infrared dielectric response obtained from light demodulation at multiple harmonics of the AFM tapping frequency, we find that amorphization caused by the nominally 0.5 nm HIB extends throughout the entire 26.5 nm thickness of the cuprate film and by ∼500 nm laterally. This unexpectedly widespread damage in morphology and electronic structure can be attributed to a helium depth distribution substantially modified by the internal device interfaces. Our study introduces AFM-SNOM as a quantitative tomographic technique for noninvasive 3D characterization of irradiation damage in a wide variety of nanoscale devices. [ABSTRACT FROM AUTHOR]

Abstract: The in-plane magnetoresistance (MR) in atomically smooth La2−x Sr x CuO4 thin films grown by molecular-beam-epitaxy was measured in magnetic fields B up to 9T over a wide range of temperatures T. The films, with x=0.03 and x=0.05, are insulating, and the positive MR emerges at . The positive MR exhibits glassy features, including history dependence and memory, for all orientations of B. The results show that this behavior, which reflects the onset of glassiness in the dynamics of doped holes, is a robust feature of the insulating state. [Copyright &y& Elsevier]

The magnetic correlations within the cuprates have undergone intense scrutiny as part of efforts to understand high-temperature superconductivity. We explore the evolution of the magnetic correlations along the nodal direction of the Brillouin zone in La2-xSrxCuO4, spanning the doping phase diagram from the antiferromagnetic Mott insulator at x=0 to the metallic phase at x=0.26. Magnetic excitations along this direction are found to be systematically softened and broadened with doping, at a higher rate than the excitations along the antinodal direction. This phenomenology is discussed in terms of the nature of the magnetism in the doped cuprates. Survival of the high-energy magnetic excitations, even in the overdoped regime, indicates that these excitations are marginal to pairing, while the influence of the low-energy excitations remains ambiguous. [ABSTRACT FROM AUTHOR]