Onset of superconductivity in the two-dimensional limit

Haviland, D. B.; Liu, Y.; Goldman, A. M.

doi:10.1103/physrevlett.62.2180

Cited by 760 publications

(594 citation statements)

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“…5d represents the threshold normal-state sheet resistance h/4e 2 , or 6.5 kΩ/□ for a superconductor-insulator transition. 38 Only the Al-rich samples have normal-state sheet resistance below the dashed line; these might thus exhibit superconductivity. The sheet carrier density is around 10 14 /cm 2 for all the samples, close to the expected value of 1.7 × 10 14 /cm 2 .…”

Section: Resultsmentioning

confidence: 99%

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Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

et al. 2017

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Advancements in nanoscale engineering of oxide interfaces and heterostructures have led to discoveries of emergent phenomena and new artificial materials. Combining the strengths of reactive molecular-beam epitaxy and pulsed-laser deposition, we show here, with examples of Sr 1+x Ti 1-x O 3+δ , Ruddlesden-Popper phase La n+1 Ni n O 3n+1 (n = 4), and LaAl 1+y O 3(1+0.5y) /SrTiO 3 interfaces, that atomic layer-by-layer laser molecular-beam epitaxy significantly advances the state of the art in constructing oxide materials with atomic layer precision and control over stoichiometry. With atomic layer-by-layer laser molecular-beam epitaxy we have produced conducting LaAlO 3 /SrTiO 3 interfaces at high oxygen pressures that show no evidence of oxygen vacancies, a capability not accessible by existing techniques. The carrier density of the interfacial two-dimensional electron gas thus obtained agrees quantitatively with the electronic reconstruction mechanism.npj Quantum Materials (2017) 2:10 ; doi:10.1038/s41535-017-0015-x INTRODUCTION Technological advances in atomic-layer control during oxide film growth have enabled the discoveries of new phenomena and new functional materials, such as the two-dimensional (2D) electron gas at the LaAlO 3 /SrTiO 3 interface, 1, 2 and asymmetric three-component ferroelectric superlattices. 3,4 Reactive molecular-beam epitaxy (MBE) and pulsed-laser deposition (PLD) are the two most successful growth techniques for epitaxial heterostructures of complex oxides. PLD possesses experimental simplicity, low cost, and versatility in the materials to be deposited. 5 Reactive MBE employing alternately-shuttered elemental sources (atomic layerby-layer MBE, or ALL-MBE) can control the cation stoichiometry precisely, thus producing oxide thin films of exceptional quality. [6][7][8] There are, however, limitations in both techniques. Reactive MBE can use only source elements whose vapor pressure is sufficiently high, excluding a large fraction of 4d and 5d metals. In addition, ozone is needed to create a highly oxidizing environment while maintaining low-pressure MBE conditions, which increases the system complexity. On the other hand, conventional PLD using a compound target often results in cation off-stoichiometry in the films. 9, 10 In this paper we present an approach that combines the strengths of reactive MBE and PLD: atomic layer-by-layer laser MBE (ALL-Laser MBE) using separate oxide targets. Ablating alternately the targets of constituent oxides, for example SrO and TiO 2 , a SrTiO 3 film can be grown one atomic layer at a time. Stoichiometry for both the cations and oxygen in the oxide films can be controlled. Although the idea of depositing atomic layers by PLD has been explored since the early days of laser MBE, 11,12 we show that levels of stoichiometry control and crystalline perfection rivaling those of

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Section: Resultsmentioning

confidence: 99%

“…The dashed line in d is the quantum resistance limit h/4e 2 . 38 The dashed line in e indicates the theoretical value of sheet carrier density for 10 unit-cell films with different stoichiometry under the assumption of pure electronic reconstruction. 31 …”

Section: Methodsmentioning

confidence: 99%

Constructing oxide interfaces and heterostructures by atomic layer-by-layer laser molecular beam epitaxy

et al. 2017

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“…Examples include transitions in quantum Hall systems [3], localization in Si-MOSFETs (metal oxide silicon field-effect transistors; Ref. [4]) and the superconductor-insulator transition in two-dimensional systems [5,6]. Both classical and quantum critical points are governed by a diverging correlation length, although quantum systems possess additional correlations that do not have a classical counterpart.…”

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confidence: 99%

Scaling of entanglement close to a quantum phase transition

Osterloh¹,

Amico

Falci

et al. 2002

Nature

1,808

2,051

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In this Letter we discuss the entanglement near a quantum phase transition by analyzing the properties of the concurrence for a class of exactly solvable models in one dimension. We find that entanglement can be classified in the framework of scaling theory. Further, we reveal a profound difference between classical correlations and the non-local quantum correlation, entanglement: the correlation length diverges at the phase transition, whereas entanglement in general remains short ranged.Classical phase transitions occur when a physical system reaches a state below a critical temperature characterized by a macroscopic order [1]. Quantum phase transitions occur at absolute zero; they are induced by the change of an external parameter or coupling constant [2], and are driven by fluctuations. Examples include transitions in quantum Hall systems [3], localization in Si-MOSFETs (metal oxide silicon field-effect transistors; Ref. [4]) and the superconductor-insulator transition in two-dimensional systems [5,6]. Both classical and quantum critical points are governed by a diverging correlation length, although quantum systems possess additional correlations that do not have a classical counterpart. This phenomenon, known as entanglement [7], is the resource that enables quantum computation and communication [8]. The role of the entanglement at a phase transition is not captured by statistical mechanics -a complete classification of the critical many-body state requires the introduction of concepts from quantum information theory [9]. Here we connect the theory of critical phenomena with quantum information by exploring the entangling resources of a system close to its quantum critical point. We demonstrate, for a class of one-dimensional magnetic systems, that entanglement shows scaling behaviour in the vicinity of the transition point.There are various questions that emerge in the study of this problem. Since the ground state wave-function undergoes qualitative changes at a quantum phase transition, it is important to understand how its genuine quantum aspects evolve throughout the transition. Will entanglement between distant subsystems be extended over macroscopic regions, as correlations are? Will it carry distinct features of the transition itself and show scaling behaviour? Answering these questions is important for a deeper understanding of quantum phase transitions and also from the perspective of quantum information theory. So results that bridge these two areas of research are of great relevance. We study a set of localized spins coupled through exchange interaction and subject to an external magnetic field (we consider only spin-1/2 particles), a model central both to condensed matter and information theory and subject to intense study [10]. FIG. 1. The change in the ground state wave-function in the critical region is analyzed considering ∂ λ C(1) as a function of the reduced coupling strength λ. The curves correspond to different lattice sizes N = 11, 41, 101, 251, 401, ∞. We choose N odd to avoid the sub...

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“…This mobility dependent metal-to-insulator transition can be partly understood with the above-discussed Ioffe-Regel criterion in the 3D context. It is also well known that 2D metallic films turn insulating once their sheet resistance becomes similar to or larger than the quantum resistance (h/e 2  26 kΩ) as the thickness is reduced, due to enhanced surface scattering and other disorder effects [45] , [53]. Altogether, this comparison clearly shows that the WAL 1-to-0 transition observed in the low mobility samples whose surface Fermi levels are far from the surface-hybridization gap at the Dirac point is due to enhanced disorder in the ultrathin regime and not due to the gap opening at the Dirac point.…”

Section: Weak Anti-localizationmentioning

confidence: 99%