Pressure Induced Quantum Phase Transitions in Metallics Oxides and Pnictides
Bibliographic record
Abstract
Quantum phase transitions occur as a result of competing ground states. The focus of the present work is to understand quantum criticality and its consequences when the competition is between insulating and metallic ground states. Metal-insulator transitions are studied by means of electronic transport measurements and quantum critical points are approached by applying hydrostatic pressure in two different compounds namely Eu$_2$Ir$_2$O$_7$ and FeCrAs. The former is a ternary metal oxide and the latter is a ternary metal pnictide. \n\nA major component of this work was the development of the ultra-high pressure measurements by means of Anvil cells. A novel design is introduced which minimizes the alignment accessory components hence, making the cell more robust and easier to use.\n\nEu$_2$Ir$_2$O$_7$ is a ternary metal oxide and a member of the pyrochlore iridate family. Resistivity measurements under pressure in moissanite anvil cells show the evolution of the ground state of the system from insulating to metallic. The quantum phase transition at $P_c\\sim6$ GPa appears to be continuous. A remarkable correspondence is revealed between the effect of the hydrostatic pressure on Eu$_2$Ir$_2$O$_7$ and the effect of chemical pressure by changing the R size in the R$_2$Ir$_2$O$_7$ series. This suggests that in both cases the tuning parameter controls the $t_{2\\textrm{g}}$ bandwidth of the iridium $5d$ electrons. Moreover, hydrostatic pressure unveils a curious cross-over from incoherent to conventional metallic behaviour at a $T^* >$ 150 K in the neighbourhood of $P_c$, suggesting a connection between the high and low temperature phases. The possibility of a topological semi-metallic ground state, predicted in recent theoretical studies, is explained. \n\nFeCrAs is a ternary metal pnictide with Fermi liquid specific heat and susceptibility behaviour but non-metallic non-Fermi liquid resistivity behaviour. Characteristic properties of the compound are explained and compared to those of superconducting pnictides. Antiferromagnetic (AFM) order sets in at $\\sim125$ K with the magnetic moments residing on the Cr site. Pressure measurements are carried out in moissanite and diamond anvil cells in order to suppress the AFM order and resolve the underlying electronic transport properties. While AFM order is destroyed by pressure, the non-metallic non-Fermi liquid behaviour is shown to be robust against pressure.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".