Existence Solutions for a Class of Schrödinger-Maxwell Systems with Steep Well Potential
Abstract
In this paper, we are concerned with the system of the Schrödinger-Maxwell equations where λ, b > 0 are constants, and 3 < p < 6. Under appropriate assumptions on V and K, we prove the existence of positive solutions in the case 3 < p < 4 via the truncation technique. Moreover, suppose that V may change sign, we also obtain the multiplicity of solutions for the case 4 < p < 6.
1. Introduction and Main Results
On the potential V, we make the following assumptions:
(V1) V ∈ C(R3, R) and V is bounded below.
(V2) there exists a constant c > 0 such that the set {x ∈ R3 : V(x) ≤ c} is nonempty and meas{x ∈ R3 : V(x) ≤ c} < +∞, where meas denote the Lebesgue measure in R3.
(V3)Ω = intV−1(0) is nonempty and has smooth boundary and .
In recent years, system (1) has been widely studied under various conditions on V and K. The greatest part of the literature focuses on the study of the system for V and K being constants or radially symmetric functions. We refer the reader to [2–9].
When the potential V(x) is neither a constant nor radially symmetric, in [10, 11], the existence of ground state solutions is proved for 3 < p < 6. In [12–14], the existence of nontrival solution is obtained via the variational techniques in a standard way under the following condition:
(V4) V ∈ C(R3, R), where a0 > 0 is a constant. Moreover, for any M > 0, meas{x ∈ R3 : V(x) ≤ M} < +∞, where meas denote the Lebesgue measure in R3.
By using a linking theorem, the authors obtained the existence of nontrivial solutions. Nextly, Gu, Jin, and Zhang [19] investigated the existence of sign-changing solutions for system (3). By using the method of invariant sets of descending flow, the multiple radial sign-changing solutions are obtained in the subquadratic case as λ small. For more results about the Schrödinger-Poisson systems, we refer the reader to [20–23] and the reference therein.
Here, we should point out that for the power-type nonlinearity f(u) = |u|p−2u, in order to get the boundedness of a (PS) sequence, the methods heavily rely on the restriction p ∈ (4, 6). Meanwile, the condition (V1) − (V3) cannot guarantee the compactness of the embedding of H1(R3) into the Lebesgue spaces Ls(R3), s ∈ [2, 6). This prevents from using the variational techniques in a standard way. Motivated by the works mentioned above and [24–28], in the present paper, we are mostly interested in sign-changing potentials and consider system (1) with more general potential V, K, and the range of p. Our main results are as follows:
Theorem 1. Suppose that V ≥ 0, (V1)- (V3), , K(x) ≥ 0, and 3 < p < 4 hold. Then, system (1) possesses at least a nontrivial solution for b small and λ large.
Remark 2. It is known that it is difficult to get the boundedness of a (PS) sequence when dealing with the case p ∈ (3, 4). To overcome the difficulty, motivated by [24, 25], we use the truncation technique to obtain a bounded Cerami sequence for b small. In this case, the conditions (V4) and (K1) of Theorem 1.3 in [23] cannot be used. Moreover, in the process of proving the convergence of a bounded Cerami sequence, we use the observation that the condition K ∈ L3(R3) ∪ L∞(R3) makes the less strong influence of the nonlocal term K(x)ϕu (The conclusions remain valid if K ∈ L2(R3)). In this sense, Theorem 1 can be viewed as an improvement of Theorem 1.3 in Zhao et al. [23].
Theorem 3. Suppose that (V1), (V2), K ∈ L3(R3) ∪ L∞(R3), K(x) ≥ 0, and 4 < p < 6 hold. Then, system (1) possesses infinitely many distinct pairs of nontrivial solutions whenever λ > 0 is sufficiently large.
2. Preliminaries
In view of (V1), (V2), the quadratic form is weakly continuous. We have the following proposition.
Proposition 5 ([26], Lemma 8). Suppose (V1), (V2), and V ≠ 0. Then, for each fixed j,
- (i)
μj(λ)⟶0 as λ⟶+∞
- (ii)
μj(λ) is a nonincreasing continuous function of λ, where is sequence of positive eigenvalues of problem (P) satisfying μ1(λ) ≤ μ2(λ) ≤ ⋯≤μj(λ)⟶∞ as j⟶∞ and the corresponding eigenfunctions .
Let
Then,
Moreover dim for every fixed λ > 0.
Evidently, the action functional J belongs to C1(Eλ × D1,2(R3), R) and its critical points are the solutions of system (1). It is easy to know that J exhibits a strong indefiniteness, namely, it is unbounded both from below and from above on infinitely dimensional subspaces. This indefiniteness can be removed using the reduction method described in [29], by which we are led to study a one variable functional that does not present such a strongly indefiniteness.
By the proposition 2.3 in [12], we know that (u, ϕ) ∈ Eλ × D1,2(R3) is a critical point of J if and only if u is a critical point of I and ϕ = ϕu.
To complete the proof of our theorem, we need the following results.
Theorem 6 (see [30].)Let X be a real Banach space with its dual space X∗, and suppose that J ∈ C1(X, R) satisfies
Theorem 7 see ([31], Theorem 9.12). Let E be an infinite dimensional Banach space and let I ∈ C1(E, R) be even, satisfy (PS), and I(0) = 0. If E = V ⊕ X, where V is finite dimensional and I satisfies.
(I1) there are constants ρ, α > 0 such that , and
(I2) for each finite dimensional subspace , there is an such that I ≤ 0 on ,
then, I possesses an unbounded sequence of critical values.
Lemma 8 ([17], Lemma 2.3). The function ϕu possess the following properties:
- (1)
The mapping u⟶ϕu maps bounded sets of Eλ into bounded sets of D1,2(R3);
- (2)
If un⇀u in Eλ, then in D1,2(R3);
- (3)
The mapping u⟶ϕu : Eλ⟶D1,2(R3) is continuous.
3. Proof Of Theorem 1
Lemma 9. Suppose that 3 < p < 4 and (V1) − (V3),V(x) ≥ 0 and , K(x) ≥ 0 hold. Then,
- (i)
there exists a v ∈ Eλ\{0},with J(v) < 0
- (ii)
there exists M > 0 independent of T, λ and b such that , where , Γ = {γ ∈ C([0, 1], Eλ): γ(0) = 0, γ(1) = v}
Proof. For any t > 0, by (19), we have
- (iii)
since there exists a constant M > 0 (independent of T, λ and b) such that .
Lemma 10. Suppose that 3 < p < 4 and (V1), (V2) hold. Then, there exists α > 0 such that .
Proof. For any u ∈ Eλ, we have
Since p > 3, we conclude that there exists ρ > 0 such that J(u) ≥ α > 0 for all u ∈ Eλ with
From Lemmas 9 and 10 and Theorem 6, we thus deduce that there exist a Cerami sequence {un} ⊂ Eλ such that
Lemma 11. Let 3 < p < 4, V(x) ≥ 0, (V1) − (V2), K(x) ≥ 0, and K ∈ L3(R3) ∪ L∞(R3) be satisfied. Then, there exists Λ > 1 such that for each λ ∈ (Λ, ∞), if {un} ⊂ Eλ is sequence satisfying (32), then {un} has a convergent subsequence in Eλ for b small enough.
Proof. Let {un} be a Cerami sequence satisfying (32). Let , we show that . We first prove that . Suppose by contradiction that there exist a subsequence of {un}, still denoted by {un}, such that , we obtain
which is a contradiction by Lemma 9. Suppose that there exists no subsequence of {un} which is uniformly bounded by T. Then, we deduce that . We handle the case of K ∈ L3(R3) (The conclusions remain valid if K ∈ L∞(R3)). By (22), we obtain
This is contradiction by choosing b sufficiently small. Since , passing to a subsequence if necessary, we can assume that there exists u ∈ Eλ such that un⇀u, inEλ . In view of the Sobolev embedding theorems and Lemma 8, un⇀u inEλ implies.
Furthermore, for any φ ∈ Eλ, we have
In fact, if K ∈ L∞(R3), we just need to show that
Note that
Moreover, in view of the Sobolev embedding theorem, un⇀u implies that
Hence, for large n, we obtain
Consequently,
From above inequality and (39), one has
Then, J′(un)⟶0 implies that
Let vn≔un − u. It follows from (V1), (V2) that
Moreover, let 0 < α < min{(6 − p/2), 1}, 2 < p < 6. Then, 2 < 2(p − α)/2 − α < 6. By the Sobolev inequalities and Hölder inequality, one has
We know
Letting Λ > 0 be so large that the term in the brackets above is positive when λ ≥ Λ, we get vn⟶0 in Eλ. Since vn = un − u and vn⟶0, it follows that un⟶u in Eλ. This completes the proof.
4. Proof Of Theorem 3
In this section, while V is sign-changing, we study the existence of solutions of (1) for the case 4 < p < 6 and give the proof of Theorem 3. Without loss of generality, we assume that b = 1.
Lemma 13. Let (V1), (V2), K(x) ≥ 0, and K ∈ L3(R3) ∪ L∞(R3) be satisfied. Then, there exist α, ρ > 0 such that Iλ(u) ≥ α for all with .
Proof. By proposition 5, for each fixed λ > Λ, there exists a positive integer nλ such that μj(λ) ≤ 1 for j < nλ and μj(λ) > 1 for j ≥ nλ. Thus, for any , we have
for all , where . Since p > 2, the conclusion follows by choosing ρ sufficiently small.
Lemma 14. Let (V1), (V2), K(x) ≥ 0, and K ∈ L3(R3) ∪ L∞(R3) be satisfied. Then, for any finite dimensional subspace , there is a large r > 0 such that Iλ(u) < 0 on .
Proof. Since all norms are equivalent in a finite dimensional space, there is a constant b1 > 0 such that
By (22), there is a constant CK > 0 such that
Hence, for all ,
Since p > 4, there is a large r > 0 such that I(u) < 0 on .
Lemma 15. Let (V1), (V2), K(x) ≥ 0, and K ∈ L3(R3) ∪ L∞(R3) be satisfied. Then, there exists Λ > 1 such that, for each λ ∈ (Λ, ∞), Iλ satisfies the (PS)c condition.
Proof. Let {un} be a (PS)c sequence, that is Iλ(un)⟶c and . If {un} is unbounded in Eλ, up to a subsequence, we can assume that
If w = 0, since is weakly continuous, we have
a contradiction. If w ≠ 0, then the set Ω = {x ∈ R3 : ω(x) ≠ 0} has the positive Lebesgue measure. For x ∈ Ω, one has|un(x)|⟶∞ as n⟶∞, Fatou’s lemma shows that as n⟶∞. Thus, by (22), we obtain
This is a contradiction. This implies {un} is bounded in Eλ. Going if necessary to a subsequence, we can assume that un⇀u in Eλ. The following proof is similar to the proof of Lemma 11. We omit details of this.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgment
This work is supported partially by the Foundation of Baoshan University (BYPY202016).
Open Research
Data Availability
No data were used to support this study.