Effects of disorder on Harris-criterion violating percolation

Fayfar, Sean; Bretaña, Alex; Montfrooij, Wouter

doi:10.1103/physreve.104.034110

Cited by 3 publications

(4 citation statements)

References 21 publications

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“…We note here that this protected type of percolation [55] is the one that describes the clusters that form [33] in heavily doped Ce(Ru 0.755 Fe 0.245 ) 2 Ge 2 . Of course, a fleeting distribution of Kondo temperatures is not the same as a permanent distribution, nor is stoichiometric CeRu 2 Si 2 truly quantum critical; for that we need [22] 3.5% rhodium doping on the ruthenium sites.…”

Section: Ac Susceptibilitymentioning

confidence: 69%

“…is known as the percolation threshold. This particular type of percolation is referred to as protected percolation and falls into its own universality class [33,[55][56][57]. We see from Fig.…”

Section: Quantum Critical Systems and Percolationmentioning

confidence: 97%

“…This number corresponds to the percolation threshold for protected percolation. [55] For large clusters, somewhere in the neighborhood of 1% of the moments may end up not being compensated, as we detail below. The main consequence of cluster formation is that the entities that give rise to the susceptibility signal are far less numerous than the number of Ce-ions in the sample: there are far fewer clusters than there are unit cells, and there are far fewer uncompensated moments on a cluster than there are compensated moments on a cluster.…”

Section: Ac Susceptibilitymentioning

confidence: 99%

“…The appearance of clusters with a super spin leads to a very natural explanation for the high-moment value peak in the ac-susceptibility, as well as the overall small level for the average moment. We performed computer simulations to model the protected percolation network [55] described in Section 1.4 in order to determine the cluster super spins for a given cluster distribution. We chose a lattice of size 400 × 400 × 400 magnetic sites using a body-centered nearest neighbor topology.…”

Section: Ac Susceptibilitymentioning

confidence: 99%

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Spontaneous cluster formation in stoichiometric quantum critical systems

Bretana¹

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Metallic systems with magnetic ions embedded which have been prepared to undergo a second-order phase transition at zero Kelvin (called the quantum critical systems) historically appear to fall into two distinct categories: (chemically) heavilydoped systems in which the unusual properties can be attributed to a disorder-induced distribution of Kondo shielding temperatures, and (nearly) stoichiometric systems where the departures from Fermi-liquid theory have been attributed to intrinsic instabilities. We show that this distinction between doped and stoichiometric systems is no longer a clear-cut boundary and that magnetic clusters associated with a distribution of Kondo shielding temperatures found in the heavily doped quantum critical Ce(Fe0:755Ru0:245)2Ge2 are also present in CeRu2Si2, a stoichiometric system close to a quantum critical point. By revisiting published data on CeRu2Si2 and comparing them to the results of Ce(Fe0:755Ru0:245)2Ge2, we show that clusters consisting of Ce-ions with their moments aligned with their neighbors exist in both systems at low temperatures and dominate the macroscopic response of these systems. We show these clusters form from a distribution of Kondo shielding temperatures which naturally arises from a distribution in inter-ionic separations; the chemical doping of ruthenium in Ce(Fe0:755Ru0:245)2Ge2 and zero-point motion in stoichiometric CeRu2Si2. We show that the dominant physics which drives heavily-doped systems, namely spontaneous formation of mag netic clusters, also plays a leading role in the response of homogenous systems. We investigate the presence of these spontaneous clusters in the heavily studied YbRh2Si2 where neutron scattering data have not been published. We show that the specific heat and susceptibility are naturally interpreted when ordered magnetic clusters are taken into account. Thus, cluster formation appears to be ubiquitous at the quantum critical point. We end with potential implications of the findings (that small changes in interionic separations ends up dominating the macroscopic response) to another class of highly correlated electron systems: the cuprate high Tc superconductors. We speculate that ionic displacements associated with hole doping leads to a pathway for the formation of Cooper pairs. We show that this pathway leads to an explanation for the many experimental observations, such as the striped phase and the hourglass dispersion.

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Section: Ac Susceptibilitymentioning

confidence: 69%

Section: Quantum Critical Systems and Percolationmentioning

confidence: 97%

Section: Ac Susceptibilitymentioning

confidence: 99%

Section: Ac Susceptibilitymentioning

confidence: 99%

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Spontaneous cluster formation in stoichiometric quantum critical systems

Bretana¹

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Hyperuniformity in Ashkin–Teller model

Mukherjee,

Mohanty

2024

J. Phys.: Condens. Matter

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We show that equilibrium systems in d dimension that obey the inequality dν > 2, known as Harris criterion, exhibit suppressed energy ﬂuctuation in their critical state. Ashkin-Teller model is an example in d = 2 where the correlation length exponent ν varies continuously with the inter-spin interaction strength λ and exceeds the value d/2 set by Harris criterion when λ is negative; there, the variance of the subsystem energy across a length scale l varies as l d-α with hyperuniformity exponent α = 2(1 − 1/ν). Point conﬁgurations constructed by assigning unity to the sites which has coarse-grained energy beyond a threshold value also exhibit suppressed number ﬂuctuation and hyperuniformiyty with same exponent α.

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