Photography on Selenium

Selényi, P.

doi:10.1038/161522a0

Nature

1948

DOI: 10.1038/161522a0

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Photography on Selenium

P. Selényi¹

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Cited by 5 publications

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“…However this is a strongly dissipative system with no direct access to the symmetry breaking mechanism necessary to study the robustness of asymmetric states. In addition, previous theoretical studies14,15 have interpreted the puzzling spectral properties of a gas of pyramidal molecules that date back to the 50s16, in terms of the occurrence of a QPT with parity symmetry breaking.…”

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Quantum phase transitions with parity-symmetry breaking and hysteresis

et al. 2016

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Symmetry-breaking quantum phase transitions play a key role in several condensed matter, cosmology and nuclear physics theoretical models [1][2][3] . Its observation in real systems is often hampered by finite temperatures and limited control of the system parameters. In this work we report, for the first time, the experimental observation of the full quantum phase diagram across a transition where the spatial parity symmetry is broken. Our system consists of an ultracold gas with tunable attractive interactions trapped in a spatially symmetric double-well potential. At a critical value of the interaction strength, we observe a continuous quantum phase transition where the gas spontaneously localizes in one well or the other, thus breaking the underlying symmetry of the system. Furthermore, we show the robustness of the asymmetric state against controlled energy mismatch between the two wells. This is the result of hysteresis associated with an additional discontinuous quantum phase transition that we fully characterize. Our results pave the way to the study of quantum critical phenomena at finite temperature 4 , the investigation of macroscopic quantum tunnelling of the order parameter in the hysteretic regime and the production of strongly quantum entangled states at critical points .Parity is a fundamental discrete symmetry of nature 6 conserved by gravitational, electromagnetic and strong interactions 7 . It states the invariance of a physical phenomenon under mirror reflection. Our world is pervaded by robust discrete asymmetries, spanning from the imbalance of matter and antimatter to the homo-chirality of DNA of all living organisms 8 . Their origin and stability is a subject of active debate. Quantum mechanics predicts that asymmetric states can be the result of phase transitions occurring at zero temperature, named in the literature as quantum phase transitions (QPTs) 1,4 . The breaking of a discrete symmetry via a QPT provides also asymmetric states that are particularly robust against external perturbations. Indeed, the order parameter of a continuous-symmetry-breaking QPT can freely (with no energy cost) wander along the valley of a 'mexican hat' Ginzburg-Landau potential (GLP) by coupling with gapless Goldstone modes 9 . In contrast, the order parameter of discrete-symmetry-breaking QPTs is governed by a one-dimensional double-well GLP 10 . The reduced dimensionality suppresses Goldstone excitations, and the order parameter can remain trapped at the bottom of one of the two wells. This provides a robust hysteresis associated with a first-order QPT.Evidence of parity-symmetry breaking has been reported in relativistic heavy-ions collisions 11 and in engineered photonic crystal fibres 12 . Observation of parity-symmetry breaking in a QPT has been reported for neutral atoms coupled to a high-finesse optical cavity 13 . However, this is a strongly dissipative system, with no direct access to the symmetry-breaking mechanism necessary to study the robustness of asymmetric states. In addition, previous the...

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Quantum phase transitions with parity-symmetry breaking and hysteresis

et al. 2016

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Effect of structural defects on optical properties of amorphous selenium films

Kotkata

Abdel-Wahab

1990

J Mater Sci

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Spontaneous Symmetry Breaking: Variations on a Theme

Jona-Lasinio¹

2010

Progress of Theoretical Physics

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Spontaneous symmetry breaking (SSB) is a widespread phenomenon in several areas of physics. In this paper I wish to illustrate some situations where spontaneous symmetry breaking presents non obvious aspects. The first example is taken from molecular physics and is related to the paradox of existence of chiral molecules. The second case refers to a Dirac field in presence of a magnetic field. Gusynin, Miransky and Shovkovy have shown that Nambu-Jona-Lasinio (NJL) models, where SSB of chiral symmetry takes place for the nonlinear coupling over a certain threshold, in presence of a magnetic field exhibit SSB for any value of the coupling. They called this phenomenon magnetic catalysis. I will discuss this problem in 2 + 1 dimensions from an operatorial point of view and show that the basic phenomenon is a double pairing induced by the magnetic field in the vacuum for any value of the mass. This pairing provides the environment responsible for chiral symmetry breaking in NJL models with very weak nonlinearities. The third case illustrates briefly SSB in stationary nonequilibrium states and its possible relevance in natural phenomena.

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Photography on Selenium

Cited by 5 publications

References 1 publication

Quantum phase transitions with parity-symmetry breaking and hysteresis

Quantum phase transitions with parity-symmetry breaking and hysteresis

Effect of structural defects on optical properties of amorphous selenium films

Spontaneous Symmetry Breaking: Variations on a Theme

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