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Insulator phases of BoseFermi mixtures induced by intraspecies nextneighbor interactions
by Felipe GómezLozada, Roberto Franco, Jereson SilvaValencia
Submission summary
Authors (as registered SciPost users):  Jereson Silva 
Submission information  

Preprint Link:  https://arxiv.org/abs/2309.05594v2 (pdf) 
Date submitted:  20240726 16:48 
Submitted by:  Silva, Jereson 
Submitted to:  SciPost Physics 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Computational 
Abstract
We study a onedimensional mixture of twocolor fermions and scalar bosons at the hardcore limit, focusing on the effect that the intraspecies nextneighbor interactions have on the zerotemperature ground state of the system for different fillings of each carrier. Exploring the problem's parameters, we observed that the nonlocal interaction could favor or harm the wellknown mixed Mott and spinselective Mott insulators. We also found the emergence of three unusual insulating states with charge density wave (CDW) structures in which the orders of the carriers are out of phase with each other. For instance, the immiscible CDW appears only at halffilling bosonic density, whereas the mixed CDW state is characterized by equal densities of bosons and fermions. Finally, the spinselective CDW couples the bosons and only one kind of fermions. Appropriate order parameters were proposed for each phase to obtain the critical parameters for the corresponding superfluidinsulator transition. Our results can inspire or contribute to understanding experiments in coldatom setups with longrange interactions or recent reports involving quasiparticles in semiconductor heterostructures.
Author indications on fulfilling journal expectations
 Provide a novel and synergetic link between different research areas.
 Open a new pathway in an existing or a new research direction, with clear potential for multipronged followup work
 Detail a groundbreaking theoretical/experimental/computational discovery
 Present a breakthrough on a previouslyidentified and longstanding research stumbling block
Current status:
Reports on this Submission
Strengths
 Combination of twospecies physics with more than onsite interactions.
 Discussion of multitude of insulating phases.
Weaknesses
 Motivation for multiparameter model is vague.
 The manuscript doesn't say much about the phase transitions (some order parameters are mentioned and critical values are extracted, yet what are the surrounding phases and the type of transition)
Report
In the manuscript by GomezLozada et al studies quantum phases of a onedimensional
model of BoseFermi mixtures with nextneighbor interspecies interactions.
The main interest is in insulating phases, as a main result, three incommensurate
insulators are discussed. These are the immiscible charge density wave state, the mixed
CDW state and the spinselective CDW state. The study is carried out using the density
renormalization group technique and considers several filling fractions.
BoseFermi mixtures are one of the systems that are experimentally accessible
with quantum simulator plattforms while there are also a number of experimental
systems that yield extended Hubbard models or even longrange interactions.
There is also interest in CDW states or unusual isulating states, from a broad
range of angles. Thus this work certainly has a timely context.
However, as with all model studies that involve many parameters, one wonders about the
specific motivations for these multiparameter models and the significance of the
results. Whenever there is one concrete experiment then certainly using very complex
models are justified, whenever entirely new physics emerges, the same holds. In the present
version, the motivation for this work is not spelled out in the most convincing way.
Certain other comments may warrant modifications of the manuscript, see the detailed list.
Overall, the manuscript may be publishable provided some improvements are implemented.
Requested changes
1 Improve motivation for multiparameter model.
2 Terminology: Merely adding nearestneighbor interactions does not
justify the tem "nonlocal interactions" in my understanding. Please
attempt a more precise definition.
3 Note that CDW states with periodicities larger than two are wellestablished in quantum magnetism ("magnetization plateaux") and multiorbital models. Perhaps these analogies could be mentioned.
4 It is not entirely clear how the numerical accuracy is controlled. What is actually done? Is the maximum truncation error crucial or the sweepdependent bond dimension? Please also provide definitions of the entropy/energy error.
5 Regarding Fig. 10, it is not entirely clear whether this is a schematic plot or obtained from numerical data. Also in Fig. 1: why are there only straight lines?
Recommendation
Ask for minor revision
Strengths
1 identifying phases with insulating and density wave character in BoseFermi mixtures in one dimension
2 a rather large scan over parameter space in a model that has plenty of tuning knobs
Weaknesses
 given the large local Hilbert space, the DMRG convergence is difficult
 no discussion of phase transitions
 no discussion of gapless phases; ie, a lot of physics is missing
 as all parameters are in a regime of very large potential energy compared to kinetic energy, how much of the phase diagrams can be understood from meanfield or Gutzwiller types of approaches?
 I find it hard to believe that no supersolids nor phases like CDW+superfluid are found.
Report
In "Insulator phases of Bose–Fermi mixtures induced by intraspecies nextneighbor interactions" the authors look at density wave structures in 1D BoseFermi hubbard models. They employ DMRG and provide several scans over bosonic chemical potentials at fixed fermionic densities. Most of the found density wave structures can be thought of small unit cells in which the bosonic and fermionic densities form commensurate combinations. The results are therefore not very surprising; in fact, the interesting physics in these models is usually found when tuning away from these nearclassical configurations. In this sense I do not think that the paper meets the standards of a Scipost Physics paper. Either the authors can add something truly novel and unexpected, or they should consider a journal of substantially lower rank.
additional minor remarks:
 given the hardcore nature of the bosons, what is their difference from the fermions up to a trivial JordanWigner factor? I have not understood the differences between the presented results and the putative ones of the same system consisting of a 3component hardcore bosonic system
 on p4, when referring to cold atoms (refs 8485), one should also include the scattering lengths as those cannot be chosen at will
 in Fig 1, I am confused about the "white areas" mentioned in the caption. What is meant with that? I only see white areas and lines.
 Fig 2b: is there a fermionic charge gap?
 Fig 2b: why is this referred to as incommensurate? If we take 6 lattice sites, we will definitely find an integer number of particles.
 Fig 6a, what is the small feature at rho_B = 0.2?
 Fig 11b,c: what is the meaning of the tiny plateau at rho_b = 0.4?
Requested changes
On top of the comments made above I think the paper would benefit from a table summarizing the phases found and their respective order parameters
Recommendation
Accept in alternative Journal (see Report)